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THE BOYS’ BOOK OF 
ELECTRICITY 


IN THE SAME SERIES 


THE BOYS’ BOOK OF CHEMISTRY 

A SIMPLE EXPLANATION OF UP-TO-DATE 
CHEMISTRY 

Together with Many Easily Made 
Experiments 

By CHARLES RAMSEY CLARKE 


THE BOYS’ BOOK OF PHYSICS 

A SIMPLE EXPLANATION OF MODERN 
SCIENCE 

With Easily Made Apparatus and Many 
Simple Experiments 

By CHARLES RAMSEY CLARKE 
and SIDNEY AYLMER SMALL 


Illustrated by the Authors and Charles E. 
Cartwright 


E. P. DUTTON & COMPANY 
















How Electricity is Made and Delivered. 




















































THE BOYS’ 

BOOK OF ELECTRICITY 


A SIMPLE EXPLANATION OF 
THE MODERN IDEAS ABOUT 

ELECTRICITY 

WITH MANY SIMPLE EXPERIMENTS 


BY 


SIDNEY AYLMER SMALL 


PROFUSELY ILLUSTRATED BY THE AUTHOR 
AND CHARLES E. CARTWRIGHT 



NEW YORK 

E. P. DUTTON & COMPANY 
681 Fifth Avenue 



Copyright, 1923 
By E. P. Dutton & Company 


All Rights Reserved 


QC52jT 

,S<55 


Printed in the United States of America 


©C1A759096 

H0 ' J 23 IU23 



PREFACE 


<% 


In the last decade so many new facts have been dis¬ 
covered about electricity, such a great number of new 
ideas in the theory of electricity have been argued out 
to the point where scientists agree to accept them, that 
the old explanations may be dropped and new ones put 
in their place. 

New books must therefore be written, and here is a 


book for you boys that uses the latest facts and theories, 
yet explains them in simple language. 

Luckily, these new ideas make electricity much easier 
to understand, so that now you may learn why and how 
electrical things work. 

I hope that you will have as much fun and profit in 
reading this book and doing the experiments as I have 
had pleasure in writing it. 

Sidney Aylmer Small. 


CONTENTS 


CHAPTER PAGE 

I. Introduction. 1 

II. Getting Down to Business .... 19 

III. What Electricity Is.35 

IV. Where Electricity Came From ... 53 

V. Behavior of Electrical Charges . . 67 

VI. Portable Sources of Current . *. 95 

VII. Measuring Electricity. 127 

VIII. How Electricity Comes to Us . . . 171 

IX. Magnetism.189 

X. Dynamos, Motors and Transformers . 213 

XI. Familiar Things. 241 

XII. Radio. 277 

Glossary .323 

Index .....331 





















CHAPTER I 


INTRODUCTION 

Why This Book Was Written 
The Broken Wire 
What is in a Lamp Cord 
The House Wiring 
Resistance or Rheostat 
Reading Electrical Books 
The Bright Idea of a New Book 
Putting the Idea Over 
About Pictures and Diagrams 
Let’s Go 
Your Lab. 

The Tools You Need 
Joining Wires 
Sources of Current 
Dry Cells 
Storage Battery 
A Safety Device 
Using the House Current 
The Transformer 
The Reducer 

The Reasons for Experiments 
Seeing is Believing 
A Help to Understanding 
Trying Anything Once 
Hook-Ups 



' . » 













The Boys 5 Book of Electricity 

CHAPTER I 

INTRODUCTION 

“What is the matter?” said Mr. Peter Elmer when 
he saw that Junior and Mrs. Elmer were in earnest 
conversation. “Oh, Peter,” replied his wife, “the elec¬ 
tric cord that goes to the transformer of Junior’s elec¬ 
tric train must be broken. There was a short circuit 
or something and Junior had to stop playing with the 
train.” 

“Mother, that is a rheostat, not a transformer, and 
that is a wire, not a cord,” shouted Junior. 

“I would not shout at my mother,” said Mr. Elmer. 
“Also, are there not two wires in that cord?” 

“Why, the man said we had a three-wire system in 
the house,” cried Mrs. Elmer. 

“Well,” replied Junior’s father, “what we need is 
some good book that explains in a simple way about 
electricity. Perhaps we can find out the difference 
between a transformer and a rheostat, and how long 
circuits such as from here to the power-house, can 
have short circuits.” 

The following evening at dinner Junior said that his 
Science teacher had explained a lot of things to him, 
but that when told all at once it was too much to 
remember. 

“Never mind, Junior,” said his father, “I have three 
good books on electricity in a package on the hall table. 

1 


2 


THE BOYS' BOOK OF ELECTRICITY 


After I have had my coffee we shall hunt up the ex¬ 
planations about electrical trains, wires, short circuits, 
and the electrical things about the house.” 

The hour of bedtime for Junior found a not fully 
satisfied family. The verdict was that just exactly the 
book they wanted for Junior was not there. “Probably 
there ain’t no such book,” joked Dad. 

It was then that Junior made the suggestion. ""Why 
not get my Uncle Sidney to write an electrical book for 
me ? I always understand things when he explains them 
to me.” 

""Fine,” answered his father, ‘"Your Uncle Sidney 
has been teaching electricity for twenty-five years to 
prep school boys and he has also taught men in a big 
university. He is the fellow to write a book for you 
and other boys. We shall ask him. Let us do it now. 
Get him on the telephone and we shall try to make him 
say yes.” 

Thus the idea of this book had its birth, and, boys, 
here is the book. In it you will learn what electricity 
is, what it will do, and why it does these particular 
things. Your puzzles about amperes and volts, about 
why the electric locomotive reverses when you move a 
certain lever, why you can’t run a train from an in¬ 
duction coil, nor silver-plate spoons with alternating 
current, all these and many more will be explained. 

Many interesting experiments which will help you to 
understand electricity have been devised. These are 
fully described with all the details so that you can 
readily follow the instructions and easily do the ex¬ 
periments. 

Whenever a picture or a diagram will make things 
clearer, one is there for you. Whenever I use a word 
that I think you will not understand, I shall either ex¬ 
plain it right there or ask you to turn to the Appendix 
where you will find a list of words and their meanings. 
But all this talk isn’t the book, so “Let’s go.” 



INTRODUCTION 


3 


Your Lab. —If you are to understand electricity, 
it will be a great help to do some experiments. An 
electrical lab. need not occupy much space, and yet if 
you have a lab. you will have all your tools and sup¬ 
plies in one place, and you can have each tool and 
kind of material in its own spot ready to lay your 
hand on it. 

The Tools You Need. —Your tools should be of 
medium size and fitted to your hands. When you buy 
your tools, try the “feel” of them. 

Pliers. — Side-cutting pliers are of first importance. 
They will cut wires, assist in skinning insulation from 
the ends of wires, and hold things. They are shown in 
Fig. 1A. 

Long-jawed pliers are very useful for holding flat 
metal sheets. They grip flat things much better than 
the shorter jaws of other pliers. Illustrated in Fig. IB. 

Combination pliers. —An excellent tool that has a 
medium length of jaw. It has a wire cutter so placed 
as not to interfere with the use of the jaws for holding 
things. This tool is shown in Fig. 1C. With side¬ 
cutting pliers, if you hold anything firmly, the cutting 
edge is apt to dent the surface. The long-jawed pliers 
have no side cutter to do any damage while you are 
holding things, but they will not hold flat plates firmly, 
because like all ordinary pliers their jaws open in a V 
shape. The combination plier is often called a parallel- 
jaw plier for the jaws open and close, always parallel 
to each other. They will grip flat things very firmly. 

Round-nosed pliers are used for bending sheet metal 
and wires; also for smoothing kinks out of wires. Fig. 

All these pliers should be either the five-inch size or 
that size which fits your hand the best. Beware of big 
tools for they will not go into small corners. 

Screw-Drivers. —There are many different shapes 
of screw-drivers; short, long, thin and fat-handled, 


4 


THE BOYS' BOOK OF ELECTRICITY 



Fig. 1a. The Tools You Will Need. 




















INTRODUCTION 


5 



Fig. 1b. The Tools You Will Need. 










































6 


THE BOYS’ BOOK OF ELECTRICITY 


but at the business end they are all very much alike. 
There are three sizes of ends that fit all the ordinary¬ 
sized screws. Pick up a lot of screws, large and small, 
and an examination shows that there are but three sizes 
of slots on all the screws. 

You will need one each of the two smaller sizes of 
screw-drivers. Let their lengths and the sizes of the 
handles suit your own taste in tools. One of the very 
small, slender screw-drivers will be very useful for 
getting into narrow places. 

I do not like the automobile type, ^combination tools 
for lab. work. These tools are so apt to be suitable 
for the large-sized screws, bolts and nuts, but out of 
place for the work that you will do. 

Files. —Small flat files about six inches long and 
with a surface called mill are needed to smooth off 
corners. The rat-tail or round file is used to smooth 
the inside surface of holes. You do not need tri¬ 
angular files. For a very coarse file use the broken 
hack-saw blade that you will soon have after starting 
work. 

For Holes. —While a brace with a set of bits and 
drills is a luxury that you will appreciate very much 
for quick work, I have found that a coping-saw and a 
good gimlet will replace them very nicely. See Fig. 1, 
G and H. 

. Witl1 a brace and bit you need as many bits as the 
different-sized holes you will cut. For large holes an 
extension bit would be needed. In the coping-saw and 
gimlet method, you mark the circle, drill a gimlet hole 
on the line of the outside edge of the hole, slip the saw 
blade through and then snap it into its frame. Then 
as in Fig. 2 you are ready to cut out the plug of wood 
leaving a circular hole. 

The coping-saw will cut much thicker wood than it 
was intended to cut, and we will use it in our lab as 
a wood saw. 


INTRODUCTION 7 

Hack-Saw. —For cutting metals like very heavy 
wire, rods, or plates, the hack-saw is needed. 

Tin Snips. —For sheet metal, use a pair of medium 
size tin snips, which are really very heavy scissors. 
With these you can, after a little practice, cut quickly 
and with a straight, smooth edge. 

Vises. —Bench Vise. This means a small vise that 
can be clamped on your work bench. It serves to hold 



material firmly while you hammer, file, fit, or solder 
pieces together. Fig. IK. 

Hand Vise .—This useful tool avoids a lot of work 
in awkward cramped positions. When you can’t work 
comfortably at the bench vise, clamp the work in this 
hand vise and you can hold it firmly yet twist it into 
any convenient position. The bench vise is more con¬ 
venient, if you can use it, because it leaves both hands 
free to work with. 

Hammer.—A small mechanic’s hammer is much 
better than the regular tack or nail hammer. Its wedge- 
shaped end will get down into narrow places. It should 
be light, else your experiments may not survive its 
blows. 

Clamp. —This iron screw-clamp will hold large flat 
pieces on the bench in a much more convenient position 














8 


THE BOYS’ BOOK OF ELECTRICITY 


than would the vise. It also serves to hold pieces of 
wood when glued until they become thoroughly dry. 

Wire. —You will not want to run out to purchase 
wire each time you start an experiment, nor will you 
want to buy large quantities of certain special sizes 
until you know what large pieces of apparatus you 
will be most likely to build. 

Before you begin the experiments you should pur¬ 
chase 20 feet of duplex lamp cord, size No. 14 or No. 
18. The No. 14 wire is a larger size than No. 18 and 
will offer less opposition to the current. 

You will find this cord contains two conductors each 
of which is composed of a group of fine wires. This is 
to make the wire flexible. 

Buy 20 feet of fixture wire. This is a rubber-in¬ 
sulated solid wire that is used in chandeliers. It will 
be size No. 18 and be properly insulated so as to safely 
carry a pressure of 110 volts. 

Half a pound each of single cotton-covered No. 22 
and No. 18, also a quarter pound of No. 30 single cot¬ 
ton-covered wire will complete your wire supply. To 
this add a roll of electrician’s tape. The small-sized 
roll will be a sufficient amount. 

Adhesives. —Gumstickum is what boys seem to call 
them. Shellac cut in alcohol—cut means dissolved— 
is used to insulate, protect from moisture and stick 
things together. A half pint goes a long way. Also 
buy a small can of liquid glue. Keep both shellac and 
glue tightly corked. 

Odds and Eras.-Nails, brads, screws, and metal 
strips had better be purchased as you need them. Buy 
a pound of paraffin. J 

Storeroom.—A set of empty cigar boxes, properly 
labelled on the ends, and neatly piled up, makes a fine 
storeroom for your material, and if you are so lucky 
as to have a drawer under the shelf for your tools then 
your lab. will always be in order. 


INTRODUCTION 


9 


Soldering Outfit. —A small soldering copper, the 
pound size is best, some solder in the form of wire, 
and rosin or a soldering paste that your dealer says 
does not contain acid, will be needed. For heating the 
soldering copper you may use a bunsen burner, or an 
alcohol lamp. 

Joining Wires .—For a temporary joint while you 
are experimenting you may omit the soldering, but do 
not consider any apparatus that you have made as 



finished until all joints are soldered and binding posts 
have been attached. To do a good soldering job your 
soldering copper must be prepared. File the end until 
it is clean, heat until hot, but not red hot. If the flame 
turns green take the copper out of flame at once. Rub 
some rosin or soldering paste on the tip of the copper. 
Hold the end of the wire of solder against the spot of 
rosin until a drop or two melts off. With a clean 
copper wire rub this melted solder on the soldering 
copper. The solder will spread over the end of the 
copper. You can now say that the copper is tinned. 
This bright clean tinned surface of the soldering copper 
is the part you use in soldering things. 

Clean the ends of the two wires that are to be joined, 
twist them together as shown in Fig. 3A. Use clean 
pliers. Never touch with your fingers a surface that 
is to be soldered. Rub a little powdered rosin or 












io THE BOYS’ BOOK OF ELECTRICITY 


soldering paste on the joint. Melt a drop of solder 
on the copper, and bringing the copper against the 
joint as shown, hold until the wires get heated and the 
solder adhers. Do this again on the lower surface and 
then with the hot copper rub the joint clean. Then 
when cool wrap with tape as in Fig. 3B. When start¬ 
ing to tape the joint a few narrow pieces may be cut 
and used to build up the center of the joint to the size 



of the remainder of the joint. This makes the cover¬ 
ing smoother and gives a better appearance. 

Sources of Current.— Dry Cells. —For your ex¬ 
periments you need current and at first you must have 
a perfectly safe source. Four dry cells connected up 
as shown in Fig. 4 are spoken of as being connected in 
series. Notice that each zinc can is connected to the 
carbon rod in the center of the next cell and so on. 
The two wires that go to your experiment come from 
the terminals of the battery. The positive ( +) term¬ 
inal is the carbon rod and the negative (—) terminal 
is the zinc can. 

Storage Battery. —Perhaps you have a radio A 
battery which is a storage battery. This makes a fine 
source of current. The wire that you attach to the 
binding post which is marked +, or which on many 
batteries is painted red will be your positive wire. 










INTRODUCTION 


ii 


Since a lot of damage may be done to the insides 
of the battery and also a flash of flame produced, if the 
positive and negative terminals touch each other, you 
should have some safety device. I will show you how 
to make one. Remember to make it and use it ex¬ 
actly as directed. 

The arrangement shown in Fig. 5 is a good one. 
You will find it most convenient to place the storage 
battery on the floor under the bench. Fasten a strip 
of wood from the bench to the floor and fasten the 
safety device to this strip of wood. There is then no 



Fig. 5. Hook-up for Using a Storage Battery. 


chance of metal tools coming in contact with both 
blades of the switch, which would injure the battery. 

If you must leave the battery where it is, then con¬ 
sider the safety device as part of your apparatus. At¬ 
tach the experiment to the safety device and then the 
safety device to the battery. 

A Safety Device. —On a board of convenient size 
place a porcelain, main-line, two-wire plug cut-out. 
When screwing it down do not tighten the screws be¬ 
yond the point where the cut-out is held firmly, else 
you may crack the porcelain. Buy with the cut-out 
four 3 ampere plug fuses. Place two in the sockets of 
the cut-out, reserving the others for use if one should 
melt or blow as we say. 







12 


THE BOYS' BOOK OF ELECTRICITY 


The double-pole single-throw 5 ampere knife-switch 
is attached as shown in Fig. 5. Wire up as shown and 
mark one wire + and the other —. When in use 
attach the positive or -f- pole of storage battery, the 
one usually painted red, to the -f* wire of the safety 
device. Do not allow any metal tools or stray pieces 
of wire to come in contact with the switch blades. 

The switch may have a porcelain or black composi¬ 
tion base. Do not buy poorly constructed ones. If a 
switch is loosely put together you will have bad elec¬ 
trical contacts. 

The shopkeeper would call your switch a D. P. S. T. 
5 amp. knife, all of which is easy to translate when you 
know its full name. Double-pole means that there is 
a blade for each of the two wires or poles of the bat¬ 
tery. Single-throw means that the switch opens and 
closes (throws) in only one way, controlling only one 
circuit. By 5 ampere is meant that the size of the 
switch blades is such that 5 amperes of electricity may 
be cut off and put on, or as we say, a circuit carrying 
5 amperes may be opened and closed indefinitely with¬ 
out injury to the switch. Knife refers to the type of 
switch. It opens and closes somewhat like the blades 
of a pocket knife. 

Using the House Current. —You should not at¬ 
tempt to use the house current for experiments until 
you have learned to do exactly as you are told and 
nothing but what you have read in the directions for 
an experiment. 

The storage battery has only 6 volts of pressure or 
push in it, but the electric light wires of your home 
have 110 to 120 volts of pressure. If the wires from 
the storage battery happen to touch by accident it is 
something like the bursting of a small dam across a 
small stream. But should such a thing happen to the 
wires of the house, it would be like a big dam across 
a deep lake breaking. 



INTRODUCTION 


13 


The actual danger from 110 volt house supply wires 
lies in the flash of flame you get when these wires touch 
each other. It may injure you and start a fire. When 
this happens, the fuses in the circuit are blown and 
they must be replaced before the family can get any 
service from the wires. 

For the present, if you wish to use the house supply 
for experiments, find out from the company that serves 
you whether you have alternating or direct current 
supply. If service is a. c. (alternating current) buy a 
transformer such as is used for toy electric railways. 
Should the supply be d. c. (direct current) buy a 
regulator used for the same purpose. Either of these 
when connected up as in Fig. 6 will give you a proper 
and safe voltage. 

Later on when you have become more familiar with 
electrical things I will show you how to build a 110 
volt control panel. 

The Transformer shown in Fig. 6 is connected to 
the house current by screwing the attachment plug into 
any convenient lamp socket on an alternating current 
supply line. 

As you swing the lever over to the contacts marked 
B, C, D, E and F, the pressure at the terminals H and 
K becomes greater. You will understand better why 
this is so by looking at the diagram of the interior of 
the transformer. 

Connected to the 110 volt line is a coil of many 
turns of fine wire. Only a small current flows because 
the resistance of this coil is high. This coil is wound 
on a frame of soft iron and on the same frame is 
wound a coil of fewer turns of coarser wire. 

Due to the magnetism generated by the many turns 
on the 110 volt side of the transformer, power is trans¬ 
ferred to the other coil. A much lower voltage is pro¬ 
duced because the other coil has fewer turns. 

Since the voltage depends on the number of turns 


14 THE BOYS’ BOOK OF ELECTRICITY 




//O VOLTS 


mmmmmmx. 


jLmwsmwmww 


I 


2Z 
TULL 


-.ANY EXPERIMENTS 

REDUCER 


6 /NTER/OR 
I OF 

/ REDUCER 


W EXPER/MENT- 

Fig. 6. Hook-up for Using 110 Volts. 





























INTRODUCTION 


15 


in actual use, as the lever is moved over, the voltage 
at the terminals H, K changes from 4 to 7, to 10, to 13 
and finally with the lever on F we get 15 volts at H, 
K. 

The Reducer .—When your home has a direct cur¬ 
rent supply a transformer will not operate. You then 
use a reducer. This is a resistance or an opposition to 
the high voltage of the 110 volt line so arranged that 
you can not possibly get that voltage applied to the 
trains or the experiments. 

One type of reducer is shown in Fig. 6 with its 
attachment plug screwed into a socket attached to a 
direct current service. The sliding switch regulates 
the pressure sent to the experiment. 

The interior view shows five coils of wire each of 
which uses up 22 of the 110 volts. If you should 
touch the ends of any one of these coils these 22 volts 
will send a current through you, but such a small one 
that it would not harm you. You could just feel it 
sting. 

From the diagram you will see that the binding post 
marked Full is connected by a bar to the slider S and 
that this bar does not touch the Off post. It is sup¬ 
ported there but insulated from it electrically. 

If the slider is in the position shown in the view of 
the outside of the reducer it is collecting 11 volts for 
the experiment. In the position shown in the interior 
view, the slider is collecting about 5 volts. Way over 
to the right the slider would place 22 volts of pressure 
on the experiment, and way over to the left you will 
get no pressure at all. 

Whether using the transformer or the reducer for 
experiments, consider it as a battery and connect the 
terminals of these devices to the fuse block of the safety 
device shown in Fig. 5 and attach your experiment to 
the other end of the safety device. 

This will avoid damage to the wiring of the expen- 


16 THE BOYS’ BOOK OF ELECTRICITY 


sive transformer or reducer, replacing that catastrophe 
by the blowing of a cheap fuse. 

The Reasons for Experiments.—There are two 
sides to the study of electricity, the practical and the 
theoretical, the doing of things and the knowing why 
they happen. These two aspects of science should go 
together. A very studious chap may read this book 
through before doing any construction work or ex¬ 
perimentation. I think the average fellow will want 
to try things out as he goes along. This is the better 
way, for then you see for yourself that things work the 
way the descriptions say that they will. 

Seeing Is Believing.—Facts that seem hard to 
believe when only read about become clearer when you 
talk them over with a chum; but an experiment makes 
them real facts. You get the idea then at first hand 
from Nature itself, working through your apparatus. 
Therefore do the experiments. 

A Help to Understanding.—Theories may seem 
hazy when descriptions are read. Although no ex¬ 
periment that you do may prove the theories, yet you 
get an insight into things that helps wonderfully in 
understanding them. You may sit and think getting 
no nearer an understanding. Do an experiment which 
depends on this theory for an explanation of how it 
works, and your mind will be guided along the proper 
lines and you will begin to see not only the how but 
the why of it. 

Trying Anything Once.—This is not the real 
spirit of scientific investigation. You should be will¬ 
ing to try and try. If the experiment does not work 
out as it should perhaps some little thing is at fault. 
Look over the hook-up and find the trouble. An ex¬ 
periment may be performed many times with lots of 
fun each time, and with a greater understanding of the 
principle involved. Try it thrice should be your motto. 

Hook-Ups.—If you will glance at Figs. 9 and 


INTRODUCTION 


1 7 


10 of the next chapter, you will see that they are 
simply diagrams. They show instruments and cells by 
some form that suggests the desired article to your 
mind. These drawings show how to “wire” an ex¬ 
periment or, as it is sometimes expressed, they show 
how to set up an experiment The old name for such 
drawings was “wiring diagram” and the very latest 
name is “hook-up.” 

In hook-up sketches or drawings we use “conven¬ 
tional signs” for pieces of apparatus, rather than actual 
pictures of them. We thus save a lot of time and 
when one becomes accustomed to the signs they are 
just as clear as the pictures. 

When, as in Figs. 4, 5 and 6 we are making a sketch 
of a hook-up of unfamiliar things, or perhaps I should 
say things not familiar to the other person, then we 
make actual pictures of the things. 

After doing an experiment, if you find that your 
arrangement of the pieces of apparatus was different 
from the hook-up given in the book, but that as far 
as the flow of electricity was concerned the hook-up was 
the same, then draw in your note book a hook-up of 
the experiment just as you performed it. This will 
enable you to do the experiment again without waste of 
time. 






CHAPTER II 

GETTING DOWN TO BUSINESS 


Let Us Build Something 
The Galvanoscope 
The Galvanometer 
Making a Galvanoscope 
Experiment I 

The Winding Reel 
Paraffining the Coil 
Glue, Screw or Nail 
The Frame 
Astatic Needles 
The Galvanometer Scale 
What Will We Do 
Cells Connected in Series 
Experiment 2 

Measurement of Pressure 
How Current Aeeects the Galvanometer 
Experiment 3 

Measurement of Quantity; 

Back to Theory Again 


19 








CHAPTER II 


GETTING DOWN TO BUSINESS 

Let Us Build Something. —About the first thing 
that you will want to know when you begin to ex¬ 
periment will be whether there is any current flowing, 
and in what direction it is going. Later on you will 
want a current measurer that will be quite exact, but 
for the present you can construct a galvanoscope and 
use it as mentioned above. You may also construct a 
resistance coil and a shunt which will enable you to use 
this instrument as a fairly good galvanometer . 

The Galvanoscope. —This instrument, named after 
Galvani, an Italian scientist, means an instrument mak¬ 
ing electricity visible. The Greek word skopeo, which 
we spell scope, means to see. 

The Galvanometer is an instrument that measures 
current. The Greek word metron, which we use as 
meter, means to measure. 

Experiment 1.—How to Make a Galvanoscope. 
—Cut a piece of cardboard 7^ inches long and 1J4 
inches wide. The corners must be square and the sides 
parallel. Lay this on the work bench before you and 
draw lines across it. Starting at one end draw lines at 
%, 1J4, 3#, 424 and 7^4 inches from one end. 

The cardboard will now look something like Fig. 
7A. The marks will be as shown J4 inch from each 
end, 1 inch and 2J4 inches apart. 

With a sharp knife crease deeply at all these lines* 
about one-third the way through the material. At the 
21 


22 


THE BOYS' BOOK OF ELECTRICITY 


place shown in Fig. 7 A cut a slot 1J4 inches long and 
54 inch wide. Now fold the cardboard into a frame. 
Paste the quarter inch overlaps to hold the box se¬ 
curely. Fig. 7B. 

The Winding Reel .—To properly wind this coil and 
the others that are to follow, you will avoid a lot of 
trouble from kinks in wires if you will take a few 
moments now to make a proper winding reel. 

At the right-hand side of the work bench make a 
gimlet hole. Enlarge this with the coping-saw until a 
pencil or a slender dowel rod will fit into it. Under 
the hole nail a piece of wood so that the rod cannot 
fall through. Should rod fit a little loosely in the hole, 
plug the hole with match sticks until the rod is held 
firmly. 

Over the rod slip the spool of a half pound of No. 
22 single cotton-covered copper wire. See Fig. 7C. 

Slip the fingers of your left hand into the cardboard 
frame, and leaving an end of wire about 6 inches long 
free, begin to wind the coil. Start on the left side of 
the slot. Wind a layer of 8 turns and then two layers 
more, making 24 turns in all. Secure this coil with 
some slips of electrician’s tape. 

While winding, the wire should have unwound from 
the spool smoothly as the spool revolved on the rod. 
Watch carefully for loops forming, which as you pull 
on the wire will change from the loops of Fig. 7D to 
kinks like the one in Fig. 7E. Even if you smooth out 
such a kink there is always danger that the wire will 
break at that place. The sharp bending weakens the 
metal very much. 

When the twenty-fourth turn is completed bring up 
the wire across the end of the frame so that the twenty- 
fifth turn will start next to the slot and on the right 
side of it. Secure this cross-over wire with slips of 
tape. Wind as before 24 turns in 3 layers of 8 turns 
each. The frame and coil now appear as in Fig. 7F. 



GETTING DOWN TO BUSINESS 


23 


r\soo 



Fig. 7. The Galvanoscqpe. 





























































































































24 THE BOYS' BOOK OF ELECTRICITY 


Paraffining the Coil .—This is a job that you will 
be doing quite frequently in the course of your ex¬ 
periments, so learn how to do it neatly. First tie the 
coil at several places with thread because the hot par¬ 
affin may cause the slips of tape to come off. 

In a metal cup melt enough paraffin, or parawax as 
some stores call it, to at least allow more than half the 
coil to be submerged. Melt the paraffin but do not 
heat to a higher degree of temperature. It is hot 
enough when it becomes liquid and you may easily 
heat it to a temperature hotter than boiling water. 

Using two pairs of pliers dip the frame and coil into 
the melted paraffin and hold over the cup to drain. 
When cool it will be ready to mount. The paraffin will 
protect the windings, hold them in place, and make 
them damp proof. 

Glue , Screw or Nail .—When constructing the 
wooden parts of apparatus the question arises as to 
what is the best way to fasten different pieces together. 

Gluing .—If wood surfaces are smooth, dry and free 
from grease, a very thin coat of liquid glue will serve 
to stick the pieces together as strongly as nails or screws 
would have done. Glued joints must be clamped to¬ 
gether and left in the clamp at least a day and a night. 

Such a joint is strong, has no projecting nail or 
screw heads, and apparatus fastened in this way is not 
magnetic. 

Screwing .—This is the next best method of fasten¬ 
ing wood to wood. To make a tight, strong screwed 
joint without splitting the wood requires slow and care¬ 
ful work. The following method is a good one, for it 
has been used many times on difficult jobs. 

When you buy screws of a particular length you will 
find that you can get them in many thicknesses. Select 
slender ones as they have less wedging action and hence 
less tendency to split the wood. Round-headed blued 
screws make the neatest job. The head need not be 


GETTING DOWN TO BUSINESS 


25 


sunk into the wood, and thus there is one less thing to 
do. These dark blue screws give a fine appearance at 
less cost than brass ones. 

Hold the pieces in their proper places and mark on 
the top piece where you intend to put the screws. Heat 
a steel knitting needle red hot and bum holes through 
the top piece. 

Place the pieces together again and through the holes 
in the top part mark where the screws will go into the 
lower part. Separate the pieces and with a gimlet make 
holes in the lower part. Work slowly so as not to 
exert a sidewise or splitting force. Do not press hard, 
take it easy. Do not burn the holes as the charcoal 
on the edges of the hole won’t hold the screws. 

If you are using round-headed screws place the 
pieces together and slowly twist the screws in place. 
Do not force. Enlarge the holes if necessary. Should 
you get the holes too large a sliver from a match stick, 
dropped into the holes will make the screw bite and 
secure a tight fit. 

If you are using flat-headed screws, “counter sink” 
the heads. This means make a hole to receive the head 
so that on the finished job the top of the head of the 
screw will be flush, that is level, with the wood. 

To do this, select a large wire nail whose point is 
about as large as the head of the screw. Clamp it in 
the hand vise and using it as a drill enlarge the top of 
the hole that you burned, just enough to receive the 
head of the screw. Some times heating the point of 
the nail to burn the wood will help you, but this is apt 
to discolor the wood around the hole. 

When the screw is firmly in place the head should 
be flush with the wood. Sand paper the job a little and 
a neat workmanlike result will be obtained. 

Carelessly drilled holes and unevenly driven screws 
will result in the two pieces taking a position a little 
different from that which you intended them to take. 


26 THE BOYS' BOOK OF ELECTRICITY 


This may not spoil the experiment, but you cannot be 
proud of the apparatus. 

Nails .—The only type of nail used in small apparatus 
is the brad. All slender wire nails with narrow heads 
come under this name. They are so slender that they 
will not split good wood and may be driven in, flush 
with the surface of the wood. Drive all brads straight 
down through the upper piece until the points are just 
through. Then place the pieces together and again 
drive straight down. The final blows, setting the head 
in flush, should be light ones else you will dent the 
wood. 

The Frame .—Make a wooden frame and base as 
shown in Fig. 7G. The sizes need not be just as given. 
If the available pieces of wood are somewhat near these 
sizes go ahead with them and thus save lots of time 
that otherwise would be used in cutting and trimming 
the wood. But make it neatly. Good electrical qual¬ 
ities usually go with good mechanical workmanship. 
Drill, or better yet burn the hole at M with a steel 
knitting needle or slender wire nail. Burning holes in 
thin wood has the advantage of never splitting the 
wood. Have the metal red hot at the tip, press hard 
on the wood and repeat as soon as metal cools. At 
N put a small screw eye. Put on the two binding posts 
at corners of the base board. 

Astatic Needles .—The proper way to magnetize the 
two sewing needles would be to stroke both at the 
same time. This, however, makes them so nearly alike 
that when used as a pair of astatic needles they are 
much too sensitive for us. So we will give one of 
the needles an after treatment of a couple of extra 
strokes. 

The actual process consists in holding the two needles 
together, eye to eye, point to point. Stroke, but do 
not rub, the needles with one pole of a permanent mag¬ 
net. Stroke from end to end, lift magnet and repeat. 


GETTING DOWN TO BUSINESS 




After about ten strokes, drop one of the needles and 
give the other several more strokes in same direction 
with same magnet pole as before. 

From a calling card cut a piece two inches long and 
not quite a quarter of an inch wide. Bend in a U 
similar to but not exactly the shape shown in Fig. 7 K. 
Stick the needles through from opposite sides. Tie a 
thread of darning cotton through a hole in the top. 
Hold up the combination or magnet system, as we shall 
call it, and if it does not hang straight, push the needles 
in or out, or trim the card holder. 

Slide the thread through the hole, tie end to the 
screw eye so that by turning the eye you raise and 
lower the magnet system. Raise the magnet system 
up out of the way and slip the coil and frame into 
place. The coil may wobble because it is unevenly 
wound. Block it up under each end with slips of 
cardboard or thin wood nailed to base with brads. 

Have a few lumps of paraffin ready and a warm 
soldering iron. Hold the frame in place. Lower the 
magnet system into it. Adjust the height by the screw 
eye. See that frame is so placed that the magnet system 
is free to turn. While holding the frame with left 
hand lay a few lumps of paraffin on base against coil 
frame. With the warm soldering copper melt the lumps 
of paraffin. As they cool the frame will be securely 
held to the base. The trick is to have the soldering 
copper just a little cooler than you think it ought to be. 

Solder the free ends of the coil to the binding posts. 
Give all the wood a coat of shellac. You now have a 
galvanoscope so sensitive that you will have fun finding 
currents weak enough not to send it spinning around. 

Prepare also another piece like Fig. 7K. Instead of 
the two needles, replace the lower one by a magnetized 
piece of steel knitting needle. The place of the upper 
one will be taken by a broom straw from a whisk 
broom. This magnetic system will be less sensitive 


28 THE BOYS' BOOK OF ELECTRICITY 


than the other and better adapted for the making of 
measurements of the pressure and quantity of elec¬ 
tricity. 

f v Scale for a Galvanometer. —To use the galvano- 
scope for a meter or galvanometer we equip it with the 



knitting-needle broom-straw magnetic system and a 
scale . 

As shown in Fig. 8 upon a piece of cardboard 4x5 
inches we draw a half circle, a semi-circle as it is 
also called. The diameter AB is 4 inches long. From 
O the center of AB, mark off OC and OD each 


















GETTING DOWN TO BUSINESS 


29 


inch. Draw OE at right angles to AB or as we say 
perpendicular to it. OE will of course be 2 inches 
long. At 1 inch out on OE draw the line FG as shown. 
Draw BE and find its middle point H and draw the 
line OHM. Draw the line KEM which is at every 
point 2 inches away from AB. By halving EK and 
halving the halves several times you will get a series of 
points on EK. From these points draw lines down 
towards O about as far as line AE as shown in Fig. 8. 
Mark E, 0 and K, 8 and the other points 1, 2, 3, 4, 5, 
6 , and 7. Do this on the right hand side of card. 
Draw PQ like FG. Draw FP and GQ. Cut out the 
part PFGQ with a sharp knife or scissors. Cut off 
the part of card beyond line KM. 

On the block behind the coil and frame of the gal- 
vanoscope in Fig. 7, glue slips of cardboard until when 
you lay this scale on them it will rest evenly on the 
upper surface of the coil. Place so that the point 
where O was, is where the thread is. Sounds queer 
but it’s perfectly all right. Have RS over block, KM 
towards you. When you are sure you have the posi¬ 
tion correct, then remove the scale, spread glue on the 
cardboard slips and on lower side of scale. Adjust 
scale again and place all away to dry. 

What Will We Do? Now that you have built a 
galvanoscope what shall you do with it ? That depends 
on where you are in the book. I have assumed that 
while making this instrument you have taken time to 
make a good job and that perhaps in between work on 
it you have been reading the book. 

You will not understand all about the operation of 
this instrument until you have finished Chapter X. But 
I wanted you to have it ready to experiment with and 
to be able to see how facts told in the book apply to it. 

You may do Experiments 2 and 3 now and do them 
again later on; in fact you may repeat them many times, 


30 THE BOYS’ BOOK OF ELECTRICITY 


understanding the better why things happen as they da, 
the further you are along in the reading of the book. 

Experiment 2 .—To observe the effect of connecting 
more and more cells in series; place the knitting needle 
magnetic system in the galvanoscope and turn the in¬ 
strument until the broom-straw is over the 0 mark of 
the scale. 

Look at Fig. 9. This diagram is what is called a 
hook-up. The actual pictures of things are replaced 
by certain symbols or conventional signs , as they are 
also called. G is the galvanoscope. A a coil of wire. 



A 




Fig. 9. Hook-up for Measuring Pressure. 

C a dry cell. The way they are connected so that the 
electricity from the cell goes through them all, one after 
the other, is called in series. 

To make the current flow and to stop it, or as we 
say to “break” the current, there is a push button, 
switch or telegraph key at P. 

The coil A will be the spool containing the quarter 
pound of No. 30 wire that you purchased. 

When you close the circuit , which means make a 
continuous path for the current, by the push button at 
P, I cannot tell you just what the galvanoscope will do. 

The amount the galvanoscope will move depends on 
the strength of the magnet, the weight of it and the 






GETTING DOWN TO BUSINESS 


3i 


broomstraw, how difficult it is to twist the thread of 
darning cotton and finally on the amount of wire you 
have used to connect the parts of the circuit together. 

Also if your cell is not a new one it may lack the 
proper pushing ability. 

I do not want to give you exact directions nor tell 
you too much. Remember that you are experimenting. 
To a certain extent you are off on an electrical adven¬ 
ture of your own. I wish you to try to rely on yourself 
as much as possible in this experiment. 

The galvanoscope will either move or it will not 
move. If it does not move, remove the coil A and 
connect the ends of the wires to complete the circuit. 
If the galvanoscope does not move now it is because 
there is a break in the wires some where. Find that 
break or place where the wires do not touch and repair 
the break. 

Suppose it moves a lot when you take the coil A out 
and does not move perceptibly, when the coil A is in 
the circuit. That would make me happy, for then you 
have a real job ahead of you. The job is to use enough 
of the spool of No. 30 wire wrapped on an empty 
safety-match box, so that using it as coil A, the cell 
moves the broomstraw over near the number 2 on the 
scale. 

We say then that the galvanoscope reads 2 or that 
the deflection was 2. 

When you have done this, paraffin the coil, mount 
it on a board with binding posts and label it Voltmeter 
coil A. 

Let us suppose that you have your galvanoscope 
working properly using the coil A and that one cell 
gives a convenient reading which you have written 
down. 

Open the circuit at P and not disturbing anything 
else insert another cell at C. Look back at Fig. 4 so 
that you will get them in series. Note that two cells 


32 


THE BOYS' BOOK OF ELECTRICITY 


give a greater reading or deflection as it is also called. 
The word deflection means the amount of rotation of 
the magnet from its position of rest when nothing is 
connected to the instrument to the place where it comes 
to rest after the cell or cells are connected. The straw 
pointer, of course, makes the same rotation as the 
magnet. 

The deflection really means the size of the deflection, 
so the instrument should read zero before you close 
the circuit. Then the reading with circuit closed will 
be the deflection. 

On a card, or page of your note book make a head¬ 
ing, 

Measurement of Pressure. 

Copy the hook-up of Fig. 9 neatly and then make a 
heading and table of readings like the one below. 

Galvanoscope with Coil A in Series 

Deflection of.means 1J4 volts 

Deflection of.means 3 volts 

Deflection of. .means 4volts 

Deflection of.means 6 volts 

When you had one cell in the circuit you could 
assume that the pressure, measured by a quantity called 
a volt, was 1J4 volts, so when two were used the 
pressure was twice as much. This tabulation when 
filled in by your experiment will enable you at some 
future time to find the pressure given by some other 
battery. 

How Current Affects the Galvanometer.— 
Experiment 3.—We are now preparing to observe 
what a greater quantity of electricity will do when 
tested by a galvanometer. 

Set up the apparatus as shown in Fig. 10 except 






GETTING DOWN TO BUSINESS 33 

that you are to omit the wire S. See what the galvano- 
scope does. If the reading is more than 2 on the scale 
you must use the wire S. We will call this a shunt 
and explain about shunts later. 


Fasten a piece of No. 18 wire between the binding 



posts of the galvanometer just as S is attached in Fig. 
10. How much wire? I cannot tell; it depends on 
many things, as in Experiment 2. 

You must by use of a shunt , S, reduce the current in 
the galvanoscope until its reading is about 2 on the scale. 



Fig. 11. Connecting Cells in Parallel. 


You must by experiment find out that the shorter 
the wire S is made, the more current flows through it 
and the less through the galvanoscope. The longer S 
the more the galvanoscope will read. 
















34 THE BOYS’ BOOK OF ELECTRICITY 


When you are satisfied with the reading caused by 
one cell, use two cells connected in parallel, then three 
cells connected in parallel. 

To get the parallel hook-up correct, connect the cells 
as shown in Fig. 11. 

Notice that it would be correct to say that the shunt 
S is in parallel with the galvanoscope. 

A card or notebook page should now be prepared 
with the heading: 

Measurement of Quantity. 

Copy the hook-up of Fig. 10 and make a tabulation. 

Galvanoscope with Shunt in Parallel. 


Deflection of.means current from one cell 

Deflection of.means current from two cells 

Deflection of.means current from three cells 

Deflection of.means current from four cells 


When you remove the shunt wind it on an empty 
safety match box, paraffin it and attach to a small board. 
Fasten the ends of the coil to the board allowing six 
inches of each end of the wire to be free. You can 
then easily attach the shunt directly to the galvanoscope. 
Label this coil, Ammeter Coil S. 

Back to Theory Again.—We must now leave our 
work bench and learn more about electricity so that 
we may experiment again with a greater understanding 
of what we are doing. 






CHAPTER III 


WHAT ELECTRICITY IS 

The Oed Idea 
The New Idea 
Some Proofs 

Experiment 4 
Electro Chemistry 
Experiment 5 

The Idea You Are to Get 
Experiment 6 
Clinching the Argument 
The Make-Up oe Matter 
Electrons 

Cause of Light 
Cause of Magnetism 
Atoms 

Matter Not Solid 
Experiment 7 
Experiment 8 
More About Atoms 
The Make-Up oe Electricity 
Definition of Electricity 
Protons 
Electrons 

Electrical Charges 
How to Get Charges 
Actual Methods Used 
Different Kinds of Electricity 
Static Electricity 
Static 

Current Electricity 
Juice 

Their Differences 
Direct Current 
Alternating Current 
Cycles 
Frequency 

Low Frequency 
High Frequency 
Radio Frequency 
Audio Frequency 

Electricity Known by its Effects 
35 


CHAPTER III 


WHAT ELECTRICITY IS 

The Old Idea. —Were this chapter written when 
I was a boy, one would confess ignorance as to what 
electricity really was, and say that it was something 
that did certain things; that when magnets, motors, 
lamps and such things were in operation it was a some¬ 
thing called electricity that did the work. 

Today we know more about the internal structure of 
matter, and this has led us to a knowledge of what 
electricity is. 

The New Idea. —Perhaps electricity is matter or 
matter is electricity, whichever way seems best to you. 
I feel sure that electricity is the material of which our 
world is made. “Why, how can that be?” you say. 
“There are so many different kinds of substances— 
sugar, salt, gold, lead and so on; surely if they were 
all made of the same thing they would be alike.” I do 
not blame you for thinking this, but let us think over 
some things. 

Some Proofs. —I can tell you of some things com¬ 
posed of the same substance and yet acting quite dif¬ 
ferently. We are now about to take a little side path 
and roam into chemistry for just a few minutes. This 
is perfectly all right, for the chemists will tell you that 
electricity is the thing that makes their chemicals work. 

You need not do these experiments, as they are not 
electrical ones in the sense that you use the word elec¬ 
trical; they are chemical ones. Should reading them 
create a desire to read up about chemicals and do some 
chemical experiments, buy a copy of “The Boys' Book 
37 


38 THE BOYS' BOOK OF ELECTRICITY 

of Chemistry” and you will have a delightful and 
profitable time with it. 

Now, to prove that things can be made of exactly 
the same stuff and yet be very different. 

Experiment 4.—Make some oxygen by dripping 
water on sodium peroxide or oxone, as it is often 
called. Fill a glass tank with this oxygen and let a leak 
between two high voltage wires take place in the tank. 
This leak is called a silent discharge. When the tank 
is opened the oxygen has turned to ozone. 

Oxygen and ozone smell differently and act differ¬ 
ently. They are two entirely different substances, yet 
each is composed of exactly the same stuff. It is as 
uncanny as if you held three dimes tightly in your hand, 
shuffled your feet over the carpet, touched your knuckles 
to the gas or electric light chandelier and after the shock 
was over opened your hand and found two bright new 
15-cent pieces, coins that you never saw before. 

To return to our oxygen and ozone experiment. 
“Yes, but,” you want to say, “did not the electricity 
do something to the oxygen and change it by putting 
electricity into it or taking it out, and thus produce 
ozone?” “Well, suppose it did?” say I. “Then some¬ 
thing with electricity is oxygen and this something with 
more or less electricity is ozone.” That suits me, for 
this is just what I believe. I believe that one stuff can 
make two different things if the amount of electricity 
in it is changed, and furthermore I say, “Perhaps the 
original stuff itself is nothing but electricity. Experi¬ 
ments by clever scientists lead us to that belief.” 

Electro-Chemistry. —“I thought this was going 
to be a book about electricity, but it seems to be chem¬ 
istry,” I h/ar my reader say. I reply that I know that 
your radio A battery and radio B battery, the battery 
that rings your door bell or the call bells and buzzers 


WHAT ELECTRICITY IS 


39 


in Dad’s office are electro-chemical devices. I know 
that all the copper wire you use is made by an electro¬ 
chemical process. So don’t worry. This little bit of 
chemistry will come in handy before you finish this 
electrical book. 

Experiment 5.—The following experiment also shows 
that the same stuff can make two different things. 

Yellow phosphorus or, as it is sometimes called, white 
phosphorus, is an amber-colored solid which catches 
fire very easily if warmed to a temperature of 95 
degrees Fahr. It must be kept under water else it fumes, 
giving off a poisonous vapor. It produces burns that 
are poisoned and hence very hard to heal. It will dis¬ 
solve in carbon disulphide. 

If this yellow phosphorus is sealed up in a retort and 
heated to 570 degrees Fahr., when it is taken out it is 
a chocolaty-red color. It is not poisonous and won’t 
catch fire until heated to 660 degrees Fahr. It won’t 
dissolve in carbon disulphide. There you are, two 
different things made of the same stuff. 

The Idea You Are to Get. —So keen am I on 
getting you to see that the idea of all materials being 
made of electricity in different amounts and different 
arrangements about the central pieces is not any harder 
to believe than any other explanation offered, that I 
will give another experiment that, like the others, is 
designed to show that the self-same stuff can make 
different materials. 

Experiment 6.—Heat some powdered sulphur so- 
gently that it melts to a pale yellow thin liquid. Raise 
its temperature from 235 degrees Fahr. slowly to 356 
degrees Fahr. and the sulphur will become a thick dark 
brown liquid so thick that you may invert the test tube 
for a few seconds and the sulphur will not run out.. 


40 THE BOYS' BOOK OF ELECTRICITY 


Heat more and the sulphur thins to a dark brown 
liquid which begins to boil at 830 degrees Fahr. Pour 
this liquid into a pan of cold water and examine it. 

You started with a hard yellow crystalline solid; you 
have had several substances and you now have a dark 
brown chewing gum-like mass, almost like rubber. 

Clinching the Argument. —I now want you to 
say, “If I do not yet believe these things he is per¬ 
fectly capable of describing another experiment." You 
are right, boys, I can tell you of another case where 
two different materials are made of the same stuff. 
So we agree, you boys and myself, that perhaps elec¬ 
tricity is the thing that all materials are made of. We 
also agree that perhaps copper, carbon, and zinc are 
composed of particles of electricity. 

The Make-up of Matter—This is just about the 
right time to grapple with molecules, atoms, and elec¬ 
trons, for looking out of the window I see something 
that gives me a bright idea. 

I see a swarm of little insects called gnats, and they 
are swirling around in a cloud. How like an atom 
they are! All of these insects seem to be whirling 
around in the cloud, but a closer view shows that near 
the centre there are a number which merely zig-zag 
forwards, backwards, and, may I say, edgewise. I 
notice some at the outer edge of the swarm that seem 
to hover near one spot. What a wonderful atomic 
model they make! Keeping this swarm in our minds 
let us discuss electrons. 

Electrons. —An electron is a definite quantity of 
negative electricity. It is also the smallest particle of 
negative electricity that exists. How big is it? It is 
so small that it is hard to tell with ordinary decimal 
fractions how small it is. Let us call it just two ten 
billionths of a centimeter in width. The weight of an 
electron is beyond me to write. When expressed as a 


WHAT ELECTRICITY IS 


4i 


fraction of a gram, it is about one million billionth of 
its size. Just how little this is I cannot imagine. Can 
you? 

These electrons are all alike, whether they live in an 
atom of copper or an atom of zinc they care not. Any 
place where one can hang its hat is home. They are 
attracted by any nucleus, and oh my, how they dislike 
each other. 

Dry cells, wet cells, storage batteries, dynamos, and 
generators all push and shove these electrons on in a 
continuous stream, when the proper conducting path 
is furnished. Reminds me of traffic on a busy day in 
a one way street where all the cars are flivvers. 

When the proper electrical path is cut and a gap is 
formed, these cells and other devices pile crowds of 
electrons up at the gap, like the street when a traffic cop 
says “Stop” and the flivvers all crowd up treading on 
each other’s tires. 

Please remember that electricity, as you know it, con¬ 
sists of tiny specks of electricity of tiny but definite 
mass and size, all alike and all repelling each other. 

You will see then that electricity can not be spread 
evenly over things, like butter on bread, but is more 
like the tiny specks of sugar when granulated sugar is 
sprinkled on bread. 

Cause of Light .—As the electrons rotate about a 
nucleus something may cause some of them to rotate 
in a smaller circle or orbit. The electron needs less 
energy to rotate now, and being a spendthrift, throws 
this extra energy, which it has, but does not need, off 
into the universe. This radiation may, under certain 
conditions, affect our eyes as light. 

Cause of Magnetism .—We firmly believe that these 
rotating specks of electricity also cause what you call 
magnetism. 

Atoms. —The materials around us are not solid. 
They are made up of separate pieces called atoms. 


42 THE BOYS’ BOOK OF ELECTRICITY 


Even the dense materials are as porous and open- 
meshed as the swarm of gnats that I was observing 
some time ago. No, I am not joking. Of course these 
materials look and feel solid, but they are not really so. 
We cannot see, nor can we feel the openings because 
they are so small. 

Let us imagine a giant a million times your size liv¬ 
ing in a world where all things are in the same propor¬ 
tion. Suppose that some day he picked a leaf off a 
mulberry tree in his world. This leaf would be three 
million inches long, which is 4 7 miles. A scientist in 
the world of giants might, by a series of most delicate 
experiments, find that a few of our silk worms were 
present on his leaf. He could not see them with his 
microscope, but certain electrical effects would indicate 
the presence of a few specks of something. More deli¬ 
cate experiments would show that when this something 
changed its position there seemed to be a dragging 
force acting on it. Further investigation would indi¬ 
cate that there was a different something forming 
around the original something. So as the silk worm 
spun its cocoon, the scientist would know that some¬ 
thing was being surrounded by something, yet could 
not see nor would he ever hope to see these some¬ 
things. 

To such a giant a piece of our honey comb would 
appear and feel solid. An old automobile radiator 
from one of our cars would also appear smooth and 
solid to him. But his scientist would tell him that it 
really was rough and was quite porous. So you see, 
things are not always what they seem. 

Matter Is Not Solid. —Experiment 7.— Turn your 
bicycle upside down so that it rests on the handle bars 
and the saddle. Just for fun thrust a pencil back and 
forth through the spokes of the rear wheel. Now turn 
the pedal rapidly and look at the rear wheel. Can you 


WHAT ELECTRICITY IS 


43 


thrust your pencil through between the spokes? No. 
They move so fast that you cannot see them nor can 
you see the spaces between them. Nor can you poke 
a pencil through. 

There you are. As I said, small pieces in rapid 
motion can give the appearance of solidity, and the non¬ 
poke-through-able property of solid bodies. 

Here is an experiment to show that solid bodies are 
either full of small holes, or else can have small holes 



Fig. 12. Apparatus for Rutherford's Experiment. 


shot through them too small for us to detect with a 
microscope. 

If the solid bodies are full of small holes it proves 
the porous structure of solid bodies. 

If the solid bodies can have tiny holes shot through 
them which we cannot find it proves that invisible things 
do exist and that when evidence of an invisible thing 
is found, its mere invisibility is no reason for disbelief. 

Experiment 8.—A glass vessel of two compartments 
was made something like Fig. 12. The partition D 
between A and B was of thin glass. When A was filled 
with helium gas (the same gas as is now used for bal¬ 
loons) no helium could be detected in compartment B. 
Evidently the thin glass wall is solid or has holes too 
small for helium gas particles to get through. 










44 THE BOYS' BOOK OF ELECTRICITY 


But when A was filled with radium emanation, then 
in B was found helium gas. It seems as if the high 
power particles, that we know radium emanation shoots 
off, could pass through the fine spaces in the glass 
structure or punch a hole in the glass so small that 
when we cleanse the apparatus and again put helium in 
A we can find no trace of it passing through to B. 
The compartment C is really a part of B and is where 
the test for helium is applied by jumping a spark across 
the terminals E and F to see if we get the peculiar color 
of helium. This experiment was devised by Rutherford. 

More About Atoms. —Scientists have proved from 
experiments on radio-active chemicals that the atoms of 
these materials explode, and shoot out alpha particles 
which have positive electrical charges in them and also 
beta particles which are negative electricity. Thus there 
is evidence of a core or nucleus in an atom made up of 
positive electricity, and electrons. 

These are in a compact mass at the center of the 
atom. Surrounding this nucleus are revolving electrons 
(specks of negative electricity, all alike), and beyond 
these a few electrons hovering in about the same posi¬ 
tion all the time. 

I have tried to give you an idea of atomic structure 
by the diagram of an atom of aluminum shown in 
Fig. 13. The proportions are wrong because the page 
is too small for the picture and I did not want to show 
you specks too small to be seen. However, you will 
get a correct impression of the cluster at the center 
composed of 26 protons and 13 electrons. Surrounding 
this is a shell of 13 electrons. 

The Make-up of Electricity.—The electrons 
which make up one half of each piece of the materials 
of this world are tiny specks of electricity. But there 
are two kinds or characters of electricity, one we call 
positive, locked up in the nucleus of all the atoms of 


WHAT ELECTRICITY IS 


45 


this world, the other we call negative, which forms the 
outer shell of all the atoms of this world. To the posi¬ 
tive specks we give the name of protons. 

Definition of Electricity.—I really dislike to 
use such a cold-blooded word as definition, but amid 


O 


O 


O £LECTR0/VS-^O 
PRO TOMS 

o 


o 

o 


o 


0 

o 


o 

Fig. 13. A Diagram of an Atom of Aluminum. 

the delightful ideas and imaginings about science, ap¬ 
pears the absolute necessity once in a while of telling 
precisely about things. Defining or giving a definition 
is merely telling precisely. One should be able to take 
pleasure in so selecting words and arranging them that 
they give a clear and exact idea of what is being talked 
about 


o °*o 

ojv.v;° 

oV.VV 


46 THE BOYS’ BOOK OF ELECTRICITY 


What are we talking about ? Electricity. Well then, 
we had better change the subject, because just plain 
electricity, the thing that makes materials what they are, 
is not what you meant when you asked, “What is elec¬ 
tricity?” You wanted to know what electrical charges, 
currents of electricity, lightning discharges, and static 
electricity all are. In a moment I shall tell you. I shall 
now take a minute pr two to tell what electricity is. 

Electricity is the stuff that makes the materials of our 
world. It comes in little tiny pieces or specks, too small 
for us to even hope to see. These specks are of two 
kinds, each quite different, yet all the specks of one 
kind are exactly alike. One kind of speck is light and 
moves nine times as fast as the heavier ones, and the 
heavier ones are about 1850 times as heavy as the 
lighter ones. Each kind likes the other kind and they 
attract each other, but dislikes its own kind and they 
repel each other. The lighter specks are called elec¬ 
trons and the heavier ones protons. 

Protons. —The heavy, slow-moving specks of one 
kind of electricity form two thirds of the nucleus or 
core of an atom of any material. 

Electrons. —The light, fast-moving specks of the 
other kind of electricity form one third of the nucleus 
or core of an atom, and all of its outer shell. 

Friction, moving magnets near wires, and certain 
chemical actions result in a separation of electrons from 
the atoms. The separated electrons and the excess of 
protons on the atoms, which have been robbed of elec¬ 
trons, form what we call electrical charges. 

Electrical Charges.—It may be a queer statement 
to make, but I am sure you will agree with me when I 
do make the statement that electricity is no good for 
anything electrical. Now, of course, you see what I 
mean. I mean that a bunch of those specks, half of one 
kind and half of the other kind, may be zinc or gold, 
may be some substance, but is not what you call elec- 


WHAT ELECTRICITY IS 


47 


tricity. The thing that gives electrical effects is a bunch 
of one kind of specks without there being as many of 
the other kind there. 

Charged bodies have more of one kind of specks on 
them than of the other kind. 

How to Get Charges. —You see now that to get an 
electrical charge you must separate the kinds of specks. 
When we wish to charge a body positively we must 
have more protons than electrons on that body. When 
a negative charge is wanted we must have more elec¬ 
trons than protons on the body or place. 

Actual Methods Used. —Friction, cells, and dyna¬ 
mos are the ordinary ways in which charges are piled 
up at places, and each of these will be fully discussed 
in the different chapters of this book. 

Different Kinds of Electricity.—People are all 
human beings, though some are calm and pleasant, 
others hot-headed and peppery in disposition. Some 
move steadily in one direction, others dash hither and 
thither. 

The different methods of producing electrical charges 
will produce different effects, and so you hear people 
talking of static, current, and high frequency electricity, 
of a. c. and d. c. They talk of current, charges, juice. 
Suppose we take a little time now and see what all 
these terms mean. We shall then be able to talk about 
electricity to our friends, knowing that we are using 
the correct words to express our ideas. 

When we say electricity we really mean a movement 
of electrons. When we say an electrical charge we 
mean too many or too few electrons at one spot. 

Static Electricity. —When charges get on insula¬ 
tors, they accumulate and we have, on account of the 
non-conductivity of the surface of these materials, elec¬ 
trons at rest. For this reason we call them static 
charges, static electricity or simply “static,” for static 
means “still.” 


48 THE BOYS’ BOOK OP ELECTRICITY 


The surface of conductors may be supplied with 
electrons so rapidly that they can not flow away. We 
then get a pile of electrons and static phenomena are 
seen even on conductors. 

Static .—-In the air there are charges of electricity. 
These charges are picked up by our antennas, and 
these charges are conducted into our radio receivers. 
They were bunches of electrons in the air, and they 
slide down our antennas like naughty youngsters down 
a bannister. They come into our sets in bunches and, 
“slam bang,” they knock the noises into our ’phones. 

Current Electricity. —A stream of electrons pass¬ 
ing along a metal or a liquid conductor is called a cur¬ 
rent. This is the method by which electrons are pushed 
into our homes and shoved along to our lamps, vacuum 
cleaners, toasters, irons, and such like. 

Juice —When quite familiar with electricity and the 
things it does, we like to refer to current electricity as 
“juice.” 

Their Differences. —To me the behavior of static 
electricity seems to indicate that at a certain spot there 
is an enormous number of electrons and somewhere 
near them an equal deficiency of electrons. The place 
where there is an excess of electrons has certain prop¬ 
erties which we call “having a negative charge.” The 
place where there is a deficiency of electrons has similar, 
yet different properties, and we say that this place “has 
a positive charge.” 

The attraction between these positive and negative 
charges is very great. Only a very poor conducting 
path can keep them apart. When these charges accumu¬ 
late the strain between them is overwhelming. Then 
the electrons rush with lightning speed towards the 
place that is positively charged. 

The force that they exert in this rush is tremendous. 
The electrons bounce off, surge and sway back and 
forth, until all becomes calm and neutral, giving us a 


WHAT ELECTRICITY IS 49 

quiet time in which to see if results have been beneficial 
or injurious. 

Wherever a condenser is used in an electrical appa¬ 
ratus, we are holding small static charges for some use¬ 
ful purpose.. With large charges holes may be punched 
in glass, mica and rubber insulation thus letting the 
electrons run wild and do damage. Trees may be split, 
houses wrecked and valuable electrical apparatus 
changed into a combination of junk and a bad smell. 

Current electricity appears to me to be a steady 
stream of electrons pushed from behind by electrical 
pressure, this pressure merely pushing, without direct¬ 
ing. It says to the electrons “Get out,” and they go. 
They go mainly by the path of least resistance, and thus 
it is that the copper wire has a current of electrons 
flowing through it. The steadiness of the stream makes 
current electricity useful for continuous operations. 
The moderate quantity of electrons is made up for by 
the continual supply of them and the moderate pressure 
behind them makes it easy to guide them in the path 
that we have decided that we want them to go. 

By offering copper wires for them to slide along or 
through and placing rubber, porcelain or mica in their 
way in other directions, we lead electrons like a pup on 
a string. 

Direct Current. —The stream of electrons from 
a cell moves in one direction. This would be called a 
direct current and is suitable for practically every elec¬ 
trical purpose. It is especially suitable for electro¬ 
plating and electro refining of metals. It is not suitable 
for use where the pressure must be automatically 
changed. 

.Alternating Current. —If you think of an elec¬ 
tric iron or toaster as being heated by the friction of 
the electrons crowding through its wire, you will rea¬ 
lize that these electrons could move in either direction 
or both directions and give a similar result. 


50 THE BOYS’ BOOK OF ELECTRICITY 


Dynamos, magnetos and all generators of electrical 
pressure using magnets, are push and pull devices that 
reverse their push at regular intervals. They all drive 
the electrons one way for a fraction of a second and 
then reverse their pressure and drive the electrons the 
other way. This kind of stream of electrons is called 
an alternating current. 

It is suitable for heating, lighting, motors and where 
automatic changes in pressure are necessary. 

Cycles. —Suppose you lived in the middle of a block 
and left the house to walk to the corner to post a letter. 
Arriving at the corner you find that the box has been 
removed. You walk back to the other corner, passing 
your house on the way. You post the letter and go 
home. 

You have reversed the direction of your walking 
twice and have made what an electrician calls one cycle. 
You did not complete the cycle until you arrived in 
front of your house facing in the same direction as 
before. When you passed on your way back to the 
other corner you had only completed half a cycle. 

Frequency. —In alternating current we speak of the 
number of cycles per second as the frequency. The 
number of times an electron reverses its direction is 
twice the number of cycles per second. To say it dif¬ 
ferently, half the number of reversals per second is 
the frequency. 

Low Frequency. —All the a. c. supplied to your home 
or to factories is of low frequency, there being 66 to 
133 cycles per second. 

High Frequency. —Under this name the frequencies 
of 30,000 to 1,500,000 are grouped. 

Radio Frequency. —The frequency of the current 
entering your radio receiving set is about 800,000. It 
is called radio frequency to distinguish it from a fre¬ 
quency that can cause a telephone to make a sound. 

Audio Frequency. —The frequencies that are audible 


WHAT ELECTRICITY IS 


5i 


(hearable) range from 16 to 5000. Above or below 
these frequencies many ears will not respond. If a cur¬ 
rent of radio frequency passed through a telephone it 
would hesitate instead of vibrate. 

Music consists of vibrations at frequencies from 100 
to 3000, speech contains frequencies from 200 to 2000. 
Because all these are audible we call them audio fre¬ 
quencies. 

Electricity Known by Its Effects.—All these dif¬ 
ferent styles of electrical charges and currents do dif¬ 
ferent things in different ways, or sometimes the same 
things but in different ways. Some of these forms of 
electrical energy are worthless for one job, but just the 
thing for another piece of work. We must therefore 
learn about them all. You now know the names of 
the forms of electricity and have a rough idea of what 
they are like. We will proceed then, to take up where 
our electrical energy comes from, how it reaches us, 
and how we harness it to do our will, what precautions 
we must take to prevent it from getting loose and doing 
damage, and at the same time study why it does the 
things that we find it doing. 



CHAPTER IV 

WHERE ELECTRICITY COMES FROM 


Nature’s Storehouse 
We Create Nothing 
Nothing is Destroyed 
Energy 

Potential Energy 
Kinetic Energy 

The Other Hale oe Our World 
Quanta 

Borrowing From Peter to Pay Paul 
Where Electricity Comes From 
Separation oe Electrons and Protons 
A Little Argument 
Isotopes 

Static Charges 
Experiment 9 
Experiment 10 
Static Everywhere 
Atmospheric Electricity 
Franklin’s Kite 
Franklin’s Statement 
Thunder Storms 
Lightning 

Lightning Rods 
Wireless Antennas 


53 





















CHAPTER IV 


WHERE ELECTRICITY COMES FROM 

Nature’s Storehouse. —We have already come to 
the conclusion that the whole world is made of elec¬ 
tricity, so why bother about where it comes from? 
True, but we are again running into our old trouble, 
that when we say electricity we do not really mean just 
electricity, but have in our minds electrical charges 
and currents. 

Yet after all, when we wonder where the electrons 
which light our homes, toast our bread and refine our 
copper come from, the answer that they have come 
from the electric light station is not going back far 
enough. The supply of electrons in this world is lim¬ 
ited and definite. If all the specks that make the mate¬ 
rials of this world were counted just half of them 
would be electrons. 

Of course we cannot count them; there are too many 
in the world to be counted, yet their number is as definite 
as if we had them all tagged and counted. 

These electrons in Nature’s storehouse are the source 
of all charges, and currents of electricity. We catch 
them, shove them, push them into crowds, pile them up 
on places where they cannot jump off as fast as they 
arrive; we jostle them along, all at high pressure and 
marvelous speed. 

We Create Nothing. —We do not manufacture 
electrons. There are the same number in the world 
today as there have always been, and there will be the 
same number years from now. All the changes from 
copper ore to copper, from zinc to zinc sulphate, from 


56 THE BOYS’ BOOK OE ELECTRICITY 


radium to lead merely change the places where the elec¬ 
trons and protons live. The electrons and protons are 
not destroyed, nor are they altered in the tiniest degree. 
They are eternal and unalterable. 

Nothing Is Destroyed. —The electrons and protons 
form other groups, and the materials will in conse¬ 
quence be known to us by different names. 

We must remember then, that in obtaining electrical 
charges or currents, we create nothing, we destroy 
nothing, but we simply change things, and during this 
change we move a bunch of electrons from one place 
to another. To do this requires energy. 

Energy. —The ability to do work is called energy. 
Energy is given out when bodies cool off, when elec¬ 
trons fall nearer the nucleus and revolve in smaller 
orbits, when bodies fall towards the earth. Energy is^ 
stored up when a body or set of bodies is under re¬ 
straint and would do something if the restraining force 
were removed. Wound up springs, a stick of dynamite, 
a suspended weight, or a bunch of electrons fenced in 
by paraffined paper are examples of stored energy. 

Potential Energy. —When energy is stored up in 
a body or set of bodies ready to do work when the 
restraining force is removed it is called potential energy. 

Kinetic Energy. —When the ability to do work is 
due to the motion of bodies it is called kinetic energy. 

The Other Half of Our World. —We are now 
able to clearly understand that a world could be made 
of matter, (specks of electricity), and that this world 
would work—or had I better say operate?—if it con¬ 
tained energy (ability to do work). A moment’s 
thought will convince you that all we do in this world 
is to push and pull matter (electricity) around, using 
up energy to do it. 

So our world, reduced to the simplest parts or ele¬ 
ments, is composed of three things: protons, electrons, 
and energy. 


WHERE ELECTRICITY COMES FROM 5 7 


Quanta. —Rather mean to spring this word so sud¬ 
denly. I did not intend to do so, but it slipped right 
off the pen. It came in so naturally, because a quantum 
is only the bit of energy that we use for a measure 
when we are considering the small quantities of energy 
which are radiated from atoms. Quanta is the proper 
plural rather than quantums. 

Borrowing From Peter to Pay Paul.—In about 
two minutes I intend to perform an experiment in 
which I shall collect a lot of electrons at one spot. 
Where shall I get the energy to do this ? Shall I get it 
from the muscles of my right arm? Yes, but could I 
use my arm vigorously had not the cook fed me well? 
I’ll tell my readers, No. So as we trace back I find 
that I get my energy from the sunshine that furnished 
the energy to warm and water the plants that made my 
food. 

It took us some time to discover that the work of 
the world is operated by borrowed energy. However, 
that is always the case. We neither create nor destroy 
matter (electrons and protons), and we neither create 
nor destroy energy. We only transform energy from 
one kind to another, making it operate our machines, 
and do our work as it changes. 

If you will turn to the Frontispiece in this book you 
will see that I have shown you how the sun hidden be¬ 
hind the clouds is the place where the light given by 
your electric lamp came from. 

Where Electricity Comes From.—The sun raises 
the water, which later on comes down as rain into the 
mountain lake. From the dam through the flume or 
penstock, the water runs down to the power house. 
There, flowing through the turbine it turns the large 
dynamo or generator. The stream of electrons at high 
pressure is guided by the transmission line in the form 
of a high voltage, alternating current, across the river 
and country to a sub-station. Here transformers re- 


58 THE BOYS’ BOOK OF ELECTRICITY 


duce the pressure low enough so that it is safe to carry 
it under ground through the suburban streets to the 
home of Mr. Elmer. In front of the garage there is 
an electric lamp, the tungsten wires of which are made 
white hot by the electrons rushing through them. Thus 
you will see that the lamp is operated by the energy of 
the sun. 

Perhaps the boy who is reading this lives where 
mountain lakes or rivers capable of being dammed are 
scarce. Then you are getting your electric light from 
the sun just the same, only the details of the process 
differ. 

Years ago the sun poured its energy in the form of 
heat on the forests; it used its ability to work in lifting 
water up, to fall later as rain, upon the trees, and thus 
wood was formed. When the wood of this luxuriant 
forest was covered with water, mud or dirt, before it 
could decay, it was turned into coal. The sun’s energy, 
locked up in this coal, is released in the furnace under 
the boiler, and carried by the steam into an engine. 
There the energy revolves a dynamo and we get a 
stream of electrons. 

Separation of Electrons and Protons. —In or¬ 
der to produce an electrical charge we may rub together 
two different substances. Some convenient ones would 
be: your comb and your hair in dry weather, your dry 
hand and the family cat’s furry back, a glass rod and 
a really truthfully silk necktie (that came from a silk 
worm), also a flannel shirt or wool trousers. Suppose 
we use the glass rod and the silk. The thin glass rod 
furnished in chemical sets is not as good as a test tube. 
If the test tube is very short you may find that most 
of the charge escapes through your hand and body to 
the ground. If you can buy a cheap towel rack, whose 
rod is glass—either the transparent or milky glass will 
do—you have a proper glass rod. It will be long 
enough to hold and rub conveniently, and the part not 


WHERE ELECTRICITY COMES FROM 59 


in contact with your hand will be large enough to hold 
a good sized charge. 

Now that you have your glass rod and piece of silk 
cloth ready for the experiment, please lay them aside 
a moment and do a little mental work. 

Think hard for a moment of the idea that these two 
materials are nothing but an enormous number of little 
pieces. When these are rubbed together the pieces at 
the surface are going to get mixed up. Also remember 
that an electron is only happy near a proton, but that 
any old proton will do. You can then understand that 
when by the rubbing you have gotten the two surfaces 
well mixed, perhaps on separating them you might take 
away some of the electrons from the glass because they 
adhere to the silk. 

A Little Argument. —Wow! Hold on! Wait a 
bit! Give the poor author a chance to explain. I only 
said perhaps. But I’ll tell you right to your face, that 
I am only waiting for the storm of protest to calm 
down, when I will tell you that this is what really does 
happen. 

I can hear the protest, that it could not happen, for 
if it did, then the surface of the glass would be changed. 
If glass is a mixture of protons, electrons and energy, 
then when you take away some electrons you have a 
new substance. Quite right, you do. 

Furthermore, possibly you are saying that those 
extra electrons are not merely smeared on the surface 
of the silk, but that the rubbing must have rubbed them 
in so as to form a coating of a new material on the silk. 
Well, you might say so. I am not so sure of this, be¬ 
cause electrons can and do exist by themselves, and so 
unless they actually are forced into the atoms which 
make up the silk there will be no new substance. 

But to return to the glass. When some of the elec¬ 
trons are torn away from a few of the atoms which 
make up the glass, we get a few particles of a new 


6o THE BOYS' BOOK OF ELECTRICITY 


substance, but a quantity too small to see and of a kind 
not possible to detect by chemistry. 

Worse and worse! Not content with all the other 
bunk, he is now trying to tell us of a substance that 
the chemists, the modem wizards, can't detect. Yes, I 
am telling you that. Ask any chemist, and he will tell 
you that this is true, and also of the 

Isotopes. —There are two kinds of chlorine, two 
kinds each of bromine, potassium magnesium, lithium, 
silicon, and six kinds of lead. These are different to 
the physicist or electrical investigator, but absolutely 
the same to the chemist. He can’t tell them apart, sim¬ 
ply because chemically they are the same. 

Substances that are chemically indistinguishable yet 
really different in their internal structure are called 
Isotopes. 

It may be possible, then, for you to rub electrons off 
the glass on to the silk and yet have the substance show 
no difference to you or to the chemist, while to the 
electrical man they are different, for the glass is charged 
positively and the silk is negatively charged. 

Well, let’s do it. 

Static Charges. —Experiment 9.—Bend a piece of 
wire into a hook at one end and fasten it into a hole 
in a block of wood so as to form a support. Tie a 
small piece of tissue paper by a silk thread to the hook. 
Warm a glass rod and a piece of silk and rub together 
vigorously. Bring the glass rod near the piece of tissue 
paper and it will be attracted. Perhaps we should say 
that there is a mutual attraction between them. 

You electrified or charged the rod by the rubbing, in 
the way previously explained, but the tissue paper had 
not been rubbed and was therefore neutral. What then 
has really happened? It must be that the excess of 
protons on the glass rod attracts an equal number of 


WHERE ELECTRICITY COMES FROM 61 


electrons over to the part of the paper nearer the rod, 
thus charging that spot negatively and making the 
further side positively charged. 

Then between the excess of protons on the glass rod 
and the excess of electrons on the nearer side of the 
paper there is an attraction. This shows that unlike 
CHARGES ATTRACT EACH OTHER. 

Experiment 10.—Perhaps you have already in Ex¬ 
periment 9 permitted the tissue paper to touch the rod. 
If not rub silk and rod again, and holding the rod near 
the paper as the paper is attracted let it touch the rod. 
It sticks for a moment and then is repelled. 

The charged paper and charged rod afford a path 
for the excess electrons on the part of the paper near 
the rod to get back to the glass rod. Since the glass 
rod was heavily charged positively, and the paper only 
had a weak negative charge, the electrons coming over 
from the paper did not make the glass rod neutral. 
The positively charged glass rod and the positively 
charged paper now repel each other. The whole dis¬ 
cussion may be followed step by step by going over 
the parts of Fig. 14. 

Have you noticed that in these experiments I did not 
tell you to use the silk with which you rubbed the glass? 
Had you tried to get an effect from the silk you would 
have obtained little or no results. Surely the silk was 
charged. Why then did it not show a charge? Just 
try the experiment again. Notice that the silk was all 
crumpled up and a great deal of its surface was in a 
very good contact with your hand. Thus the silk was 
kept neutral by the surplus of electrons flowing away 
through your body. 

Suppose you rub a fountain pen on your woolen 
trousers while the trousers are on your body. Both 
trousers and pen will become charged. The charge on 


62 THE BOYS' BOOK OF ELECTRICITY 


the end of the pen that you are not touching will stay 
there, for the hard rubber of the pen is not a conductor, 
but your trousers cannot be permanently charged. They 
are connected quite well to your body, which is a good 


/>AP ^ CLASS 



conductor, and so electrons can flow into the woolen 
trousers, thus supplying its deficiency of electrons which 
the rubbing had produced. 

Static Everywhere. —Static charges are developed 
in many places. Friction is usually the cause of their 












WHERE ELECTRICITY COMES FROM 63 


formation. Sliding your feet over woolen carpets, the 
sliding of my hand over the paper as I write, both pro¬ 
duce static charges. When I make an error and erase, 
then the vigorous rubbing produces such a gharge on 
the paper that the whole sheet will stick to my hand 
when I attempt to lay it on the pile of finished sheets. 
I find more charge is generated when I brush off the 
crumbs of paper at the end of the erasing than was 
produced by the actual rubbing with the eraser. 

Tearing a sheet of paper from a pad, if done quickly, 
will charge the sheet tom off and the pad. 

In factories the belts on the pulleys of rapidly re¬ 
volving shafts create very heavy static charges. 

A locomotive when blowing off steam through the 
safety valve electrifies the drops of water in the cloud 
of condensed steam. 

Atmospheric Electricity. —The similarity in the 
effects of lightning and those of the electric spark ob¬ 
tained from a static charge was noticed by the earliest 
investigators. 

Lightning punches holes through things opposing its 
passage, and where they are combustible, often sets 
fire to them. It can produce all the effects of heat in 
melting metals and turning them into vapor, leaving 
behind an odor of ozone. This odor may be observed 
when any electrical device that causes sparking has 
been in operation for a few minutes. 

To Franklin is given the credit of showing that all 
the stunts done by lightning were also done, although 
in a much less degree, by static charges. He did this 
by sending up a kite. 

Franklin’s Kite .—In June, 1752, Benjamin Franklin 
raised a silk kite carrying a sharp pointed wire about 
a foot long. He held the kite string by a silk ribbon, 
and to keep the ribbon dry stood within a doorway. 
To the end of the kite string was attached a metal key, 
probably the key of the door beside him. 


64 THE BOYS' BOOK OF ELECTRICITY 


He and his son watched with great interest and were 
feeling that after all nothing was going to happen. 
Finally the kite string becoming wet, and hence a con¬ 
ductor for the electrical charges, they saw the frayed 
portions of the string stand out straight. When Frank¬ 
lin’s knuckle was placed against the key a big spark 
occurred. Leyden jars were charged, lots of later ex¬ 
periments done, and finally he found that sometimes he 
was collecting positive charges while at other times 
negative charges. Thus he showed that lightning and 
static electricity are the same. 

Franklin's Statement .—To quote his own words: 
“Lightning and the spark from excited electrics are 
the same on account of giving light; color of the 
light; crooked direction; swift motion; being conducted 
by metals; noise in exploding; conductivity in water 
and ice; rending imperfect conductors; destroying 
animals; melting metals; firing inflammable substances; 
sulphurous smell (he meant smell of ozone) ; similarity 
of appearance between the brush discharge from the 
tips of masts and spars sometimes seen at sea, called 
St. Elmo’s fire by the sailors, and the slow escape from 
points on an electrical machine or a Leyden jar.” I’ll 
tell the world that old Benjamin was some careful 
and accurate scientific observer. 

Thunder Storms .—One of the most interesting 
things that is due to atmospheric charges is the thunder 
storm with its rain, lightning and noise. Each particle 
of water in the cloud seems to have acquired a charge 
when it hopped out of the body of water in which it 
lived on the earth’s surface. This charge is probably a 
small one. 

As these particles of water way up in the sky fall 
towards the earth, many touch others and unite, so 
that the charges of say eight small drops may now be 
on one drop weighing eight times as much as a single 
drop but not having eight times the surface of a single 


WHERE ELECTRICITY COMES FROM 65 


drop. The surface of the large drop is only one half 
as large as that of the eight little ones. 

The charge can only be on the surface, so the eight 
charges are squeezed into half the space and so the 
pressure is doubled. 

By the repeated union of these larger drops, the 
pressure becomes very high. Also the influence of 



the charged cloud is to accumulate a charge of the 
opposite kind of electricity on the earth beneath the 
cloud. 

Lightning. —As you will see in Fig. 15, Mr. Alli¬ 
son’s house at A is highly charged with negative elec¬ 
tricity, and the positive charge forms on the ground as 
a ring around the negative. There is danger in that 
accumulation of + and — charges, and if the pressure 
to discharge through the air is greater than the elec¬ 
trical resistance of the air, a lightning stroke will hit 
Mr. Allison’s house. 


























66 THE BOYS' BOOK OF ELECTRICITY 


Lightning Rods .—Sharp points will discharge the 
places to which they are attached. Mr. Barrow's home 
at B is protected by properly applied lightning rods. 
The sharp points at the top of these rods are con¬ 
tinually allowing the negative charges on the house 
to slip off into the air. These rods are connected to 
metallic plates buried in the ground and so the ground 
about the house is discharged. 

All this tends to discharge the house and to neutralize 
the parts of the clouds above the house. No charge, 
no lightning stroke. 

Wireless Antennas .—The aerials or antennas of 
wireless receiving and sending sets are really a protec¬ 
tion against lightning strokes. The narrow wires of 
which they are composed will tend to dissipate and dis¬ 
charge any electrical charge that a cloud is trying to 
accumulate. 

The antennas had better be permanently grounded 
by one of the vacuum devices that permits the recep¬ 
tion of the radio frequency current, yet always offers 
a nice easy path from the ground to the air for static 
charges. In the rare event that charges accumulate 
more rapidly than your antenna can get rid of them, 
when the lightning hits it finds a path to go harmlessly 
to the ground. 


CHAPTER V 

BEHAVIOR OF ELECTRICAL CHARGES 


Distribution of Static Charges 
Charges Always on Surface 
Experiment II 
Testing for Charges 
The Electroscope 
Experiment 12 

The Construction of an Electroscope 
Method of Charging 
Making a Test 
The Rule for a Test 
How to Make an Electrophorus 
Experiment 13 
Something for Nothing 
The Leyden Jar 
Its Construction 
Experiment 14 
Its Operation 

Where Does the Charge Reside 
Experiment 15 

An Explanation with Apologies 
Condensers 

An Experimental Condenser 
Experiment 16 

Capacity of a Condenser 
The Microfarad 
Building a Condenser 
Experiment 17 

Rule for Capacity of a Condenser 
Dielectrics 

Condensers Connected in Circuits 
In Parallel 
In Series 

A Bit of History 


67 









CHAPTER V 


BEHAVIOR OF ELECTRICAL CHARGES 

Distribution of Static Charges. —When a body 
is charged, we should not say that it is full of elec¬ 
tricity ; covered would be a better word to use. When 
electrons are piled up on a solid ball of conducting 
material so that it is heavily charged you have covered 
the surface only. For this reason a hollow ball of 
metal, a solid metal ball or a wooden ball covered with 
tin foil will all hold the same amount of electrical 
charge. 

When the object charged has corners, edges, or 
points, the electrons are not evenly distributed over 
the outside surface, but as shown in Fig 16, the charge 
is greatest at the corners, or edges. The sharper the 
edge, the heavier is the charge there, and at a point, 
we have such a piling up of electrons that some are 
jostled off the body. Just imagine a large jagged 
rock in a field and a crowd of boys crazy to gh on 
that rock. They pile on it two or three deep with the 
result that many are shoved off. 

If upon a ball charged with electrons a tack is placed 
point upwards, the ball will be discharged by the elec¬ 
trons sliding off this point into the air. 

Not only does an electrical charge collect on the out¬ 
side of a body, but if the inside is made the outside, 
the charge will shift. At A in Fig. 16 is shown a 
device that will give you much fun and enable you to 
fool your friends. 

Charges are Always on the Surface. — Experi¬ 
ment 11.—Following the idea of Fig. 16A, make a 
69 


70 THE BOYS’ BOOK OF ELECTRICITY 


wire ring and support of heavy wire. Secure this to a 
wooden base block. Give the base a coat of shellac. 

A bag of thin silk cloth, made in a cone shape, is 
sewed or glued to this frame. A silk thread runs 
from the point of the bag both ways. By holding this 




Fig. 16. Distribution of Static Charges. 


string taut you can pull the bag inside out without let¬ 
ting it fall. 

Rub the bag with a glass rod and test the outside 
and inside for charge. There is charge only on the 
outside. By means of the silk thread turn the bag 
inside out and testing again you will find the charge 
only on the outside. 

The very best silk for this bag is taffeta, for the 
kind of cloth called silk taffeta has a great deal of 
the metal tin in its fibers. As you can imagine, this 














BEHAVIOR OF ELECTRICAL CHARGES 71 


tin makes a conducting path from the inside to the 
outside. Since I can imagine your mother’s feelings if 
you should tell her about the tin and silk cloth, perhaps 
it would be wise to keep silent. 

Make tests at different places, especially at the point 
to find out the distribution of the charge. 

Testing for Charges. —To pick up charges we 
need a proof plane. This device with the high-sounding 
title is such a humble little thing that you can make one 
in a jiffy. 

On a circular piece of thin metal or heavy tin foil 
put a drop of glue or shellac and when nearly dry stick 
a glass rod into the drop. When dry, a little more of 
the adhesive will reinforce the joint. This sounds 
simple, is simple and always works when I do it. Since 
some of my boy friends tell me that it never works* 
and that the metal always breaks off at the slightest 
touch, I will give you another method. 

Coil a short piece of wire into a tight coil or helix, 
which is the technical name for it. Solder this coil 
at one end to the metal disk and thrust the glass rod 
into the coil. It may be knocked off the rod by rough 
treatment but it may be replaced in a jiffy. 

With the proof plane you may pick up a sample of 
any charge and bring it over to an electroscope in order 
to determine whether it is positive or negative. 

Remember that a positive charge is when electrons 
have been taken away from the atoms of the material. 
Negative charge is developed when electrons have been 
added to the atoms. 

The Electroscope. —The old standard device used 
years ago to detect the presence of electrical charge and 
to determine its positive or negative character is still in 
use today. The most eminent scientists use it for some 
of their experiments on radio-activity and the internal 
construction of matter. 


72 THE BOYS’ BOOK OF ELECTRICITY 


The Construction and Operation of an Elec¬ 
troscope.— Experiment 12.— Select a wide-mouthed 
bottle. Find a cork or rubber stopper to fit it, or 
make one of wood. With the gimlet, drill a hole 
through the cork and select a piece of heavy wire of 
sufficient length to make the support for the leaf. See 
Fig. 17. 

Cut with the tin snips or metal shears a circle of any 
metal thick enough to hold its shape and yet thin 
enough for you to cut. Sheet tin is all right. This 
circle may be about two inches in diameter; a little 
more or less makes no difference. File the edges 
smooth. 

Bend the wire over for about a half inch in a square 
hook and solder the short bent-over portion to the 
center of the metal disc. Thrust the wire through 
the cork and if it fits loosely plug tightly in the hole 
with pieces of match stick. 

Pour melted paraffin over the cork until it is com¬ 
pletely coated and the hole where the wire goes through 
is air-tight. Place the bottle on a radiator or near a 
register to get it warm and hence dry. Cut a piece 
of tin foil, aluminum foil or gold leaf about y 2 inch 
wide and 3 inches long. 

Clean the lower end of the wire, and bend with 
clean pliers to a hook. Put just two tiny dabs of 
shellac on the hook. Fold over the metal foil and 
hang on the hook. Place carefully in the warm dry 
jar, push the cork down firmly and the electroscope is 
finished. 

The cheaper the gold leaf, the easier it is to handle, 
because there is more copper in it and it is not beaten 
so thin. Gold leaf must be held between sheets of 
paper when cut. Very thin aluminum or tin foil is 
much easier to handle and makes a sturdier, though 
less sensitive electroscope. The heavier the leaves, the 
more charge is needed to move them. 


BEHAVIOR OF ELECTRICAL CHARGES 73 


Charging the Electroscope .—Most measuring or de¬ 
tecting instruments are ready for use when they leave 
the maker’s hands, but an electroscope must be prepared 
for use, or as we say, charged. 

When your electroscope was finished it was in the 
neutral, uncharged, or discharged condition. All these 
words mean the same thing. Every atom of the metal 



plate, wire and gold leaves was in its normal condition, 
which is the same as saying that each atom had its 
proper number of electrons; no more, no less than the 
exact proper number. 

Take your glass rod and rub on the silk. It will 
become charged positively. In a diagram such as is 
shown in Fig. 17A, the combination + and — sign 
means neutral. To show that the glass rod is positively 
charged in the B part of Fig. 17, we mark it with + 
signs. 
























74 THE BOYS' BOOK OF ELECTRICITY 


When the positively charged glass rod with its lack 
of electrons and excess of protons is brought near the 
electroscope, it attracts electrons from the gold leaves 
up to the metal plate. The distance from the metal 
plate to the glass rod is too great for the electrons to 
jump, or to put it another way the pressure needed to 
make them jump the space is much greater than the 
pressure that the glass rod can exert. The result is as 
shown in Fig. 17B. The gold leaves repel each other 
and separate because both are charged with the same 
Rind of charge. 

Keeping everything as it is, you must now touch the 
metal plate of the electroscope with your free hand. 
The negative charge on the plate is not affected for it 
is held by the positive charge of the glass rod. A 
charge held in this way by the influence of another is 
often called a bound charge. 

Electrons will be taken from your hand and these 
will neutralize the positive charge on the gold leaves 
making them neutral. They then no longer repel each 
other and so fall down or collapse. The electrons 
leaving your hand temporarily make it positive. All 
this is shown in C of Fig. 17. Take your hand away 
and nothing happens, nor should anything happen be¬ 
cause the electrical state of affairs in C are not altered 
when hand is removed as shown in D. 

Remove the charged glass rod and the negative 
charge in the plate, being no longer held bound, is free 
to flow all over the surface of the metal plate, gold 
leaves, and the connecting wire. The gold leaves being 
similarly charged now repel each other and separate. 
See Fig. 17 E. 

From the influence of a positive charge, the electro¬ 
scope is now negatively charged. This process of 
charging without contact with the charged body is 
charging by induction. The charge on the electroscope 
is an induced charge. 


BEHAVIOR OF ELECTRICAL CHARGES 75 


Making the Test .—Rub a stick of sealing wax upon 
woolen cloth. Bring the sealing wax near the metal 
plate of the charged electroscope. Do not touch the 
metal plate with hand or sealing wax. The gold leaves 
of the electroscope will separate further because like 
charges repel and the sealing wax carried a negative 
charge which drove more negative charge down into 
the plates. See Fig. 17F. 

The Rule for a Test .—When the leaves diverge fur¬ 
ther the tested charge is the same kind as that on the 
electroscope. When the leaves collapse the tested 
charge is of the opposite kind to that on the electro¬ 
scope. 

How to Make An Electrophorus. —You can eas¬ 
ily make a device with which you may produce good- 
sized sparks. As shown in Fig. 18, get two tin pie 
plates, one a little smaller than the other, a small bottle 
for a handle, a wood screw and piece of wood. 

Whittle the wood into a plug that will fit the neck 
of the bottle snugly. Solder the wood screw to the 
smaller pie plate; screw on the wooden plug. Push 
the bottle down firmly on the plug. The upper part 
is now finished. 

In the bottom pan we are to form a cake of sealing 
wax. If you can purchase the big one-pound sticks of 
sealing wax, you had better do so. Melt the wax in a 
small pan placed in a larger pan of water. Thus you 
will avoid burning the wax. When liquid pour into 
your pie pan and place it on a level surface to cool. 

The composition for your bottom pan may be made 
of a mixture of 6 ounces each of gum shellac and rosin, 
and 6 fluid ounces of turpentine. Melt the gum shellac 
in a double boiler, or pan in hot water. Turn out the 
fire. Stir the turpentine in. Light fire and turn very 
low. Add the lumps of rosin. Stir very gently until 
well mixed. Pour into the pie pan and set aside to 
cool. Unless you have done chemical experiments, and 


76 THE BOYS' BOOK OF ELECTRICITY 

so know how to handle hot things you should get some 
grown person to supervise the melting of the mixture. 

Experiment 13.—To produce an electrical charge 
warm the pan and cover, to drive off all moisture. Rub 
the resin cake with a piece of warm dry flannel, or any 
fur you can procure. The resin cake will become nega¬ 
tively charged. Holding the top part or cover as it is 



Fig. 18. The Electrophorus. 


called by its glass bottle insulating handle, place it on 
Ihe resin cake. The influence of the negative charge 
of the resin cake charges the bottom of the cover posi¬ 
tively and the top of the cover negatively. 

Touch with your fingers the cover and bottom tin 
at the same time. This neutralizes the free negative 
charge on the top of the cover. The cover is now 
positively charged and when removed by its insulating 
handle will give sparks when brought near any body 
that can be electrified by induction. Objects connected 
.to the ground such as gas or electric fixtures give the 











BEHAVIOR OF EEECTRICAE CHARGES 77 


best results and broad surfaces, like the wall, the worst 
results. 

To get another spark, merely replace the cover, 
touch cover and bottom tin with fingers at the same 
time and lift up cover. 

Something for Nothing? —It seems as if we were 
getting sparks for nothing, but really we are not. There 
is the work of the first rubbing, and the subsequent 
touchings and liftings. All this work added together 
is as much, and more than the energy obtained in the 
sparks. So as usual, we pay for what we get. 

You have by this time begun to wish that the small 
bunches of electrical charge obtained at each discharge 
of the electrophorus could be bottled up and then finally 
let out with one big noise. This can not be done on 
the electrophorus itself, but the separate charges can 
be accumulated until they add up to make a big charge. 

The Leyden Jar.- —In 1745 it was discovered that 
a thin glass flask partly filled with water became a col¬ 
lector of charges when held in a person’s hand. The 
source of the charges being connected with a wire to 
the water, the numerous small charges were collected 
in the flask. When the experimenter thought that 
enough had been collected, he touched the wire leading 
to the water and experienced a heavy shock. The next 
year this experiment was repeated at the University of 
Leyden, in Holland. The name Leyden Jar, given to 
it then, has stuck firmly. 

Construction of a Leyden Jar. —Find a very 
thin-walled glass bottle or what is better yet, buy an 
Erlenmeyer or Florence flask such as chemists use. 
The Erlenmeyer is cone shaped and so less likely to be 
upset. Fit a rubber stopper or a paraffined cork stopper 
to it. Drill the cork for a big wire nail. 

Some kind of a metal ball must be obtained. Its 
size and material do not count. It can be a ball from 
the end of a curtain rod or old brass bed. It can be 


1 


78 THE BOYS' BOOK OF ELECTRICITY 

a wooden or even rubber ball provided you paint it 
with shellac and then coat with tin foil. Some fellows 
form a tin foil ball about one inch in diameter by 
crumpling up sheets of tin foil. 

The ball must be attached to the top of the wire nail 
which projects from the cork. If the ball is metal, 
solder it on, but if it is only metal-coated, stick it on 
with glue, or Majors Cement. Be sure that the coat¬ 
ing of any wooden or rubber ball is connected to 
the wire by running several tin foil strips from the 
nail to the coating of the ball. To the lower end of 
the nail solder a wire long enough to reach to the 
bottom of the flask. Fig. 19A shows the completed 
jar. 

Melt some paraffin in a deep tin dish and thrust 
the flask into the melted paraffin, holding flask by the 
bottom. Coat at least the neck, or better yet what 
will be the top third of the flask. 

When cool, coat the outside with shellac up to the 
paraffin and when it is sticky, cover the entire surface 
with tin foil. When dry treat the bottom also in the 
same way. 

Pour water in which a pinch of salt has been dis¬ 
solved into the flask until it is half full Insert the 
cork and the Leyden Jar is finished. 

The Operation of a Leyden Jar.— Experiment 
14.—The jar should be held in one hand with your 
fingers in contact with the tin foil coating, or it should 
stand on a sheet of metal which is connected by a wire 
to some pipe, steam, water or gas, it matters not. 

Charge the electrophorus and bring the cover to the 
knob of the Leyden jar many times. After a dozen 
or fifteen charges have been put in and on the jar, for 
the charge is both inside and outside, you are ready 
to use the large charge that you have accumulated. 

Use the discharger shown in Fig. 19B to touch the 


BEHAVIOR OF ELECTRICAL CHARGES 79 


knob and outer coating at the same time. You will ob¬ 
tain a snappy spark. The discharger as it is shown 
consists of a curved wire twisted into a handle in the 



Fig. 19. The Leyden Jar. 


middle. This handle is fixed in a cork and the cork set 
in a small bottle. 

Where Does the Charge Reside. —It may have 
been curiosity that killed the cat of the proverb, but 
it is certainly curiosity that keeps science alive. 

Here is a pleasant situation: we charge a Leyden jar 
















So THE BOYS’ BOOK OF ELECTRICITY 


and discharge it. There are conducting surfaces or 
coatings for the inside and outside, hence, logically, the 
charge is on these coatings. Why ask any foolish 
questions, why worry? The scientific type of mind, 
however, does worry, does wonder if the perfectly 
plain reason is the true reason. Your scientist is al¬ 
ways ready to start an investigation to see if things 
are really as they seem to be. 

Now about this jar business, and the perfectly plain 
fact that the charge must be on the coatings. Franklin 
was much interested in these Leyden jars and per¬ 
formed many experiments with them. 

He found of gourse that no coatings, no Leyden jar. 
Then he made a type of jar shown in Fig. 19 at C, D 
and E. He took a tall glass tumbler as shown at D. 
Placing a sheet of thin paper in the tumbler, to prevent 
the foil from sticking, he fitted a tin foil lining. This 
lining when finished could be pulled out of the tumbler. 
Removing the paper from the tumbler he placed the 
tin foil coating back in the tumbler and pressed it 
into a good fit. When removed again it appeared as 
in C. 

In the same way he prepared a removable outer coat¬ 
ing of tin foil. When this was removed from the 
tumbler it appeared like Fig. 19E. 

You may make one yourself. A little care is re¬ 
quired. If the coatings do not fit very snugly the ex¬ 
periment will still work. 

Experiment 15.—Fit the coatings of this dissectable 
Leyden jar together and charge from the electrophorus. 
When well charged use the proof plane and the elec¬ 
troscope to show the charges that seem to be upon the 
Coatings. Now pick out the inner coating and place 
on the bench, and pick out the glass tumbler and stand 
that on the bench. In front of you you now have the 
three parts of the Leyden jar. 


BEHAVIOR OF ELECTRICAL CHARGES 81 


Test the coatings for charge. You will find none on 
them. Place the glass tumbler in the outer coating, 
the inner coating in the tumbler and test the two coat¬ 
ings for charges, and you find charges. You may ob¬ 
tain a spark by using the discharge. 

Now repeat the whole experiment but also try to 
get some charge from the glass tumbler as it stands 
on the bench with its coatings removed. You will find 
that it is charged. 

This proves that the charge resides on the glass 
and that the coatings are merely conductors to lead 
the charge up to the glass surfaces. 

An Explanation with Apologies. —Yes, I am fully 

aware that I have said two different things in the same 
chapter. I did say that static charges lived only on 
the outside of things, and I confess that I have just 
said that the charges were on the inside and outside 
of the glass. You remember that the tinny-silk or the 
silky-tin cone always had its charge on the outside. 
There seems to be a contradiction here, which must 
be investigated. 

To be exactly sure of what we are good naturedly 
bickering about, let me repeat my ideas as gained from 
actual tests. I have found that balls, metal coffee pots 
with the lids on, all tin cans with or without the tops on, 
silk stockings turned inside out, all have the charge sit¬ 
ting on the outside surface. The inside surface when 
you can get at it to test shows no charge. 

I have found that flat plates have charges on both 
sides, but as they are bent up into bowls the charge 
begins to retreat to the outside. When there is a 
metallic path the charge uses it to get to the outside. 

So the explanation of the apparent contradiction is 
that when charges are led to the inside of a non¬ 
conducting material by some metal, like sheets of tin 
foil, the charge tries to get to the outside but cannot 
/ 


82 THE BOYS' BOOK OF ELECTRICITY 


find a conducting path. I could not describe the two 
experiments at once and so apologize for keeping the 
complete statements waiting while I wrote a few pages 
about things that needed telling, right then and there. 

Static charges placed on the inside of conductors 
move to the outer surface. When placed on non¬ 
conductors they must stay where put. When, from 
the shape of the body, such as a metal bowl, the in¬ 
terior is not very far inside of the outside, then the 
charge is mostly on the outside and some on the 
interior. 

Condensers.—A device for holding many elec¬ 
trons in one place, with less tendency for them to fly 
off, is called a condenser . This sounds as if a condenser 
were an electrical cage. In one sense it is. 

Suppose we have a wire connected at one end to the 
negative terminal of a battery. The other end of the 
wire is not connected to anything, it just lies there on 
the table. You say that there is no stream of moving 
electrons. No, there is no steady stream, but for a 
moment there was a flow of electrons into the wire. We 
call this the charging current. 

When the first rush of electrons reached the end of 
the wire, it being practically a point, some of them go 
sliding off into space. The higher the pressure behind 
them the more electrons slide off the end of the wire. 
If the voltage is very high, such as they use on long 
distance transmission lines, there is a large loss of 
electrons from the end of the wire. 

If a flat plate of metal is soldered on the end of the 
wire so as to be at right angles to the wire, we have 
an electrical dam. 

The electrons come hustling down the wire, hopping 
from atom to atom, and come slam bang up against the 
plate. The pushing and shoving behind creates a pres¬ 
sure which pushes the electrons out over the plate. As 
they hop and skip up to the edge of the plate they 


BEHAVIOR OF ELECTRICAL CHARGES 83 



Fig. 20. When Electrons Come to the End of a Wire. 




































84 THE BOYS’ BOOK OF ELECTRICITY 


cannot slide off of an edge with the delightful ease with 
which they slid off the point. 

Just how many times worse an edge is than a blunt 
point like a wire, I am not prepared to say. Much de¬ 
pends on the roughness or smoothness of the edge, and 
on the thickness of the edge. The electrons will have 
at least ten times as hard a job sliding off the edge of 
the plate as they did from the end of the wire. 

An inspection of Fig. 20 should make this clearer. 
In part A of this illustration young Edward Electron 
has just slid down the hand rail of the staircase. Since 
the hand rail ended in a point young Edward has 
landed in space, just like other electrons from ends of 
wires. 

Bill Electron, when he started to slide down stairs, 
selected a staircase with a newel post at the bottom. 
You will see in part B of Fig. 20 how this prevented 
him from sliding off. In the same way the metal plate 
stopped electrons. 

When two wires end in plates which are near each 
other and the material between them is a non-conductor, 
the charges on these plates act on each other. To find 
out about these actions you must build an experimental 
condenser. 

An Experimental Condenser. —Select two blocks 
of wood about 6 inches long and 3 inches wide. Shellac 
them on all sides. Buy two tin pie plates or layer 
cake tins. Cut two slips of tin each 1 inch wide and 
3 inches long. The next step is to solder to each pie 
plate one of these tin strips. 

Now I am about to call forth that ingenuity that 
every boy has, that ability to adapt the means to the 
end. Bend the strips of tin, so that when they are 
screwed or nailed to the blocks the pie plates will stand 
upright. In order to make this possible and to make 
a secure mounting that will not wobble you may need 
to cut a groove in the block. If you find this necessary 


BEHAVIOR OF ELECTRICAL CHARGES 85 


use the coping saw to form the groove. Work slowly 
so that the turned-over edge of the cake tin will fit in 
tightly. 




THE PR/AfOPLE OF THE CONDENSER 



The condenser will look like the one in Fig. 21, al¬ 
though the actual details of the fastenings may be 
different. Connect one of them to the ball of an 
electroscope and the other to a water, steam or gas 






























86 THE BOYS’ BOOK OF ELECTRICITY 


pipe. Lacking these, connect to the electric light fixture. 
This last sentence means to the metal work that sup¬ 
ports the electric lamps. Do not connect to the electric 
light wires. 

Capacity of a Condenser. —Experiment 16.— 
Rub a glass rod on silk and bring the positively charged 
glass rod near the condenser plate A. While holding 
the glass rod near A, touch A with your fingers. Re¬ 
move your fingers and then the glass rod. In this 
way the plate A is negatively charged. That is, it 
has upon it an extra supply of electrons. 

The leaves of the electroscope should be widely 
separated. If they are not, repeat the whole process 
of charging, touching both the plate A and the knob of 
the electroscope so that it may be freed of positive 
charge. 

Now push plate B up towards A and it will be 
positively charged by induction. The electrons on A 
will drive electrons from B down the wire and down 
the pipe to the earth. The deficiency of electrons on B 
causes it to be positively charged. You will notice that 
the leaves of the electroscope are not so widely 
separated. 

The positive charge on B attracts electrons from the 
electroscope over to the plate A, thus the electroscope 
has less charge and the leaves drop nearer together. 
Push the plate B nearer and the gold leaves drop 
again. 

Here we have a quantity of electrons on A, all re¬ 
pelling each other and so the tendency to leak, or 
sneak, away from A is strong. What restrains the 
electrons on A? What makes A a sort of a cage for 
electrons? It is the combination of the plates A and B 
with an insulator between them that makes the electron 
cage, and the closer A and B are together, the closer 
are the bars of this cage. 


BEHAVIOR OF EEECTRICAE CHARGES 87 


You may add negative charges to A with a proof 
plane until a lot of extra electrons have been added 
before the electroscope will register the same pressure 
as it would connected to A with B removed. 

When B was brought near A and charged by A the 
charge on B was positive. The attraction between the 
positive on B and the negative on A drew the electrons 
to that face of A nearer to B. This left no free 
charge. The charge on the side of A nearer to B 
was bound by the charge on B. A bound charge is 
held so that its electrons cannot repel the electrons 
trying to occupy a surface near this bound charge. 
So we may add electrons to A without being opposed 
until B can no longer bind the added electrons. Then 
the excess electrons are free and oppose us when we 
try to add more. They are also free to push out along 
the wire to the electroscope, where they charge its 
leaves and make them diverge. 

Evidently the presence of a grounded conductor near 
another conductor, yet separated from it by a non¬ 
conductor, increases the capacity of this other conduc¬ 
tor for holding electrons. If this non-conductor is 
paraffin wax and the plates or conductors are very 
close together, the capacity of the combination may 
be one thousand times that of one of the plates alone. 

I have said that a body never is full of electricity. 
We can practically always force a little more elec¬ 
tricity on a surface. As charge is accumulated, the 
leakage increases. Perhaps a body is full of electricity 
or fully charged when as much leaks off as we put on. 
This would be such an inconvenient state of affairs 
and requires such an amount of electrons to place on 
the body that we have adopted a somewhat artificial 
definition of capacity. 

The Microfarad —When a condenser develops a 
tension or strain of one volt between its plates after 


88 THE BOYS’ BOOK OF ELECTRICITY 


6,300,000,000,000,000,000 electrons have been placed 
on one of the plates we say its capacity is one farad. 

This condenser is such an enormous one, that for the 
practical work of our daily electrical jobs, we use the 
term microfarad. This is one millionth of a farad. A 



$ 


B 

SHEET OF 
PARAFF1HEO PAPE/? 




D 

PA RAFF/NED PAPER 


C 

r/N FO//_ 



CARD BOARD TRAY 
Fig. 22. Construction of a Condenser. 
























BEHAVIOR OF ELECTRICAL CHARGES 89 

condenser developing 1 volt between its plates when 
6,300,000,000,000 electrons have been placed on one 
of its plates has a capacity of 1 microfarad. 

We may build a 1 mike condenser so well and of 
such good materials, that we can stow away in it three 
times its capacity before it begins to leak electricity 
all over the experiment. A mike is a slang name for a 
microfarad. 

Building a Condenser. —Experiment 17.—Melt 
some paraffin in a broad shallow pan. Select 7 sheets 
of a good quality of bond paper, such as is used for 
typewriting. These will be 8 >4 by 11 inches in size. 
A thin sheet is better than a thick one. Cut them in 
half so that you have about 14 sheets 8j4 by 5 J4 inches 
in size. Dip them in the paraffin. 

Cut tin foil into pieces as shown in A of Fig. 22. 
You will need 10 of these. 

Lay two sheets of the paraffined paper down as at 
D and on it place a tin foil sheet in the position C. 
On this another sheet of paraffined paper and then a 
tin foil sheet as in A. 

Continue to lay on alternately, sheets of paper and 
tin foil. On top put two sheets of paper. A warm 
soldering copper held very close to the edges of the 
paper will cause the paraffined edges to adhere, when 
all is cool again. 

Squeeze the projecting pieces of tin foil together 
but do not attempt to solder on a wire unless you are 
a dandy soldering man. Better fold the bunch of 
projecting ends over a wire than accidentally melt them 
offi 

Fold up a cardboard tray large enough to leave a 
little margin all around the condenser. Place the as¬ 
sembled condenser as shown in E into the box and 
pour full of melted paraffin. The condenser is now 
electrically insulated, is moisture proof and safe from 
mechanical injury, unless treated very roughly. 


90 THE BOYS' BOOK OF .ELECTRICITY 


Rule for the Capacity of a Condenser .—The greater 
the area of the metal plates of a condenser the greater 
will be its capacity. The kind of metal, or its thickness 
do not affect the capacity, for all the metal does is to 
lead the electrons to the positive charge. The square 
inches of surface of the plates gives the room for the 
electrons to “park.” (The larger the field the more 
cars can be parked in it.) 

The thinner the non-conductor which separates the 
plates the nearer the plates are together and the greater 
the capacity will be. The nearer the plates are to each 
other the stronger will be the attraction to draw and 
bind the opposite kind of charge, thus making room 
for more electrons on the plates and thus increasing 
the capacity. 

When an air-insulated condenser of one microfarad 
capacity is placed in melted paraffin and allowed to 
cool m it, when it is taken out and its capacity de¬ 
termined, we find it has increased to two microfarads. 
A condenser in which glass is used gives a capacity 
six times as large as an air-insulated condenser and 
mica is a little better than glass. 

Dielectrics .—The insulating material of a condenser 
is often spoken of as a dielectric. The value of a 
material, merely as an insulator, determines whether 
a spark can jump from one plate to the other with ease, 
or great difficulty. Aside from this property of insu¬ 
lating the plates from each other, every different 
dielectric offers a certain conductivity or resistance to 
the passage of the force between the positive and nega¬ 
tive charges. Each dielectric has its own dielectric con¬ 
stant, or specific inductive capacity as it is sometimes 
called, which determines how good a condenser may 
be made from it; good used in this sense, meaning 
higher capacity. 

Condensers Connected in Circuits. —When 
several condensers or Leyden jars, (for they are con- 


BEHAVIOR OF EEECTRICAE CHARGES 91 


densers), are connected in a circuit they are usually 
arranged to add their capacities. 

In Parallel .—If you connect all the outside coatings 
together by one wire and all the knobs leading to the 
inside coatings together by another wire, the jars are 
connected in parallel. When thus connected the capacity 
of the combination is obtained by adding up the micro¬ 
farads of each jar. 

As a formula this is, 

C = Qi + C 2 + C 3 

where C means the capacity of the group of jars or 
condensers and Q, c 2 , C 3 mean the capacity of each 
separate condenser. 

For spark coils, telephone, and radio work, clumsy 
jars are impossible. The air-paraffin and mica-insulated 
condensers are sold with two terminals attached. A 
glance at Fig. 11 in Chap. II will show you how to 
connect such condensers in parallel. Just pretend that 
the cells are condensers. 

In Series .—When the outer coating of one Leyden 
jar is connected to the knob of another the arrange¬ 
ment is called in series. The capacity of two jars 
connected in series will be found by dividing the prod¬ 
uct of their microfarads by the sum of their micro¬ 
farads. 

In a formula this is, 

Qxc 2 

C =- 

Ci + c 2 

where the letters mean the same as they did in the 
previous formula. 

What I would call regular condensers, that is radio 
condensers and such, may be connected in series very 
much like the cells in Fig. 4 Chap. I. 



92 THE BOYS' BOOK OF ELECTRICITY 

A Bit of History. —Thales, who lived 600 years 
before Christ was born, knew that amber and jet 
when rubbed with woolen cloth, would attract feathers, 
leaves and bits of straw. Pliny, writing in the year 
70, tells about such experiments. 

William Gilbert in 1600 used the word electrica to 
denote substances which acted like amber when rubbed. 
He coined the word from the Greek word “electron” 
which means amber. 

William Barlowe, in 1618 went a step further, and 
called the experiments, electrical ones. 

Otto von Guericke, in 1663, mounted a ball of sul¬ 
phur on an axle and generated charges by holding his 
warm hands against it as it was rapidly revolved. Sir 
Isaac Newton and Hawksbee, each about the same 
time, in the year 1709, used a glass globe obtaining 
the same results. 

The attraction between unlike, and repulsion between 
like charges was discovered by du Fay in 1733. He 
also showed that everything may be electrified by fric¬ 
tion. 

The Leyden jar was made by von Kleist, and then 
Watson, about 1775, succeeded in leading the discharge 
of a Leyden jar along wires. 

Benjamin Franklin from 1750 to 1760 made impor¬ 
tant experiments and devised good explanations for 
the things of which, from his observation, electricity 
was the cause. 

Faraday in 1833 showed that all electrical charges, 
whatever their source, were fundamentally alike. 

Many scientists had separately come to the conclusion 
that the study of electricity in gases and in vacuum 
would reveal a lot about the true nature of it. Crookes 
in 1872 was working along these lines. J. J. Thomson 
was hard at work in 1899 on the same subject. 

From this point the study of electrical charges was 
taken up by a great number of the scientists, in com- 


BEHAVIOR OF ELECTRICAL CHARGES 93 


bination with the work on the constitution of the mate¬ 
rials in our world. 

To Thomson, Rutherford, Wilson, Soddy and Milli¬ 
kan we chiefly owe the exact knowledge of what elec¬ 
trical charges are. 



CHAPTER VI 


PORTABLE SOURCES OF CURRENT 

Tam® Electricity in Small Packages 
Portable Sources of Electricity 
Why Cells Furnish Current 
Current From a Leyden Jar 
Experiment 18 

Cell Terminals are Charged 

Experiment 19 

What Charged the Electroscope 
The Source of the Current 
Definition of a Cell 
A Bit of History 
Why a Cell Gives Out Energy 
How Cells Push Electrons 
Making a Simple Cell 
Experiment 20 
The Actions Inside of a Cell 
Electrolyte, Electrodes, Poles 
Another Definition of a Cell 
Inside of the Cell Again 
A Talk About Copper 
Definition of An Ion 
A Talk About Zinc 

The Chemical Action in a Simple Cell 
A Practical Cell 
The Ideal Cell 

What a Simple Cell Will Not Do 
Local Action 
Experiment 21 
Amalgamation 
Experiment 22 
Experiment 23 
Polarization 
Polarization Cured 
Polarization Prevented 
The Crowfoot or Gravity Cell 
Its Chemical Action 
Ifs Electrical Action 


95 


96 THE BOYS' BOOK OF ELECTRICITY 


Electromotive Force 

Voltage 

Potential Difference 
E. M. F. of Cells 
Voltage of Cells 
Resistance of Cells 
Quantity of Electrons Obtained 
Batteries 
Types of Cells 

High Voltage Cells 
Low Voltage Cells 
Large Current Cells 
Low Current Cells 
Wet Cells 
Dry Cells 
Open Circuit Cells 
Closed Circuit Cells 
Primary Cells 
Secondary Cells 
Storage Cells 

The Lead and Acid Storage Cell 
Experiment 24 
The Practical Lead Cell 
The Alkaline Cell 
Edison Storage Cell 
Using Storage Cells 
Sizes of Storage Batteries 
The Ampere-Hour 


CHAPTER VI 


PORTABLE SOURCES OF CURRENT 

Tame Electricity in Small Packages. —I have al¬ 
ways thought of static charges as “wild” electricity, 
for it occurs everywhere, whether wanted or not. Re¬ 
minds me so much of weeds. Just for the sport of it, 
today I have been trying to dodge static charges. Did 
I ? I did not. When I walked across the floor to turn 
on the electric light I got a shock from the switch. 
When I tried to comb my cowlick it became an elec¬ 
trified shaving brush on the top of my head. When I 
wrote, the sheets of paper stuck together. I heard 
static on the radio, and finally after finishing a chapter 
of this book, I decided to change to skating togs, for 
a little exercise before dinner. Peeling my coat off in 
jig time, I developed a charge. You can't dodge these 
wild charges. 

For many purposes we want small quantities of thor¬ 
oughly tamed or domesticated electricity. A calm kind 
that will eat out of our hand, so to speak. That when 
unleashed will not go very far, nor forcibly. 

The nearest we have to this form of electricity is the 
current from cells, for from the cells of various kinds 
we get streams of electrons at low pressure. 

The best materials are zinc and copper or zinc and 
carbon. Since the zinc is used up in the work of a cell, 
it seems as if the electricity came out of the zinc. 

The best cell for the job depends upon the character 
of the work and will be fully discussed later on. 

Portable Sources of Electricity. — I seem to have 
started something, for when my son reads this I am 
97 


98 THE BOYS’ BOOK OF ELECTRICITY 


sure there will be an argument as to what I mean by 
portable. You see, yesterday he brought home a 110 
ampere hour storage battery. When he arrived he was 
“all in,” but some of the battery acid was out. When 
he rested up a bit, he told me that surely I must have 
meant that it was a 110 pound battery. However, if 
you are quite muscular, even a lead storage battery is 
portable. It was Edison himself who said that a lead 
storage battery was “very wet and very heavy.” 

We shall include in the class of portable sources, 
primary cells, secondary cells, magnetos and the motor 
generators used in automobiles. This chapter will deal 
with primary and secondary cells, or as they are more 
frequently called, cells and storage batteries. 

Why Cells Furnish Current —There are two 
places in every cell where the wires which lead to the 
work to be done should be attached. These places are 
charged. This being true, a Leyden jar or a condenser 
should furnish -current, for they have two charged 
places. When it appears that something ought to work, 
you should experiment to see whether it will or not 

Current From a Leyden Jar. —Experiment 18.— 
A piece of glass tubing of small bore is cut a little 
longer than a steel knitting needle. On it is wound a 
spiral coil of magnet wire. Keep the turns one quarter 
inch apart. Slide an unmagnetized knitting needle in 
the glass tube. Stand a Leyden jar on the wire from 
one end of the coil and arrange things so that the wire 
from the other end of the coil is not close to the jar. 
Three inches away will do. As shown in Fig. 23, with 
the discharger connect the knob of the jar to the free 
wire. The electrons will then rush through the wire 
and magnetize the needle. 

Before this experiment the knitting needle should 
have attracted both ends of the moving magnet in the 


PORTABLE SOURCES OF CURRENT 


99 


galvanoscope. After the experiment, the knitting needle 
should attract one end of the galvanoscope magnet and 
repel the other. This shows that the knitting needle is 
magnetized, and that in turn shows that current flowed 
from the Leyden jar. 

Cell Terminals Are Charged. —The places where 
the wires are attached to a cell are called terminals. 



Fig. 23 . Momentary Current from a Leyden Jar. 


One is the positive terminal, the other the negative 
terminal. These terminals are charged just as the coat¬ 
ing of a Leyden jar or the plates of a condenser are 
charged. 

Experiment 19.—Cut a circular plate of sheet metal 
the same size as the plate on your electroscope. Solder 
a wood screw to it and make a small glass bottle handle 
for it just as was done for the upper part of the electro- 
phorus, see Fig. 17. Cover its lower side with shellac. 

Arrange five dry cells in series as in Fig. 4 or use 
one 22-volt radio B battery. Attach a wire to the free 
positive terminal and one to the free negative terminal. 
If you have followed Fig. 4 exactly, simply make the 
positive and negative wires each about two feet long. 

On the metal plate of the electroscope place the shel¬ 
laced plate. Touch top and bottom plates with your 
fingers to be sure that they are neutral. 






100 THE BOYS’ BOOK OF ELECTRICITY 


Lift the upper plate by its insulating handle. Nothing 
should happen and nothing does happen. Now we are 
ready. Take the positive and negative wires of the 
battery, holding them by their insulating coverings. 
Touch one to the bottom of the bottom plate, the other 
to the top of the top plate. Remove the wires. The 
two plates are charged oppositely and these charges bind 
each other so that the gold leaves are neutral. 

Using the insulating handle, lift the top plate up. 
The gold leaves now diverge because the charge in the 
lower plate is no longer bound. This charge, now free, 
spreads over the electroscope and charges the leaves. 

What Charged the Electroscope? —Why, only 
the battery could have charged it. This shows that the 
terminals of cells carry electrical charges. Well then, 
why not touch one of the wires from a battery to the 
plate of the electroscope? Because you would get no 
results. The few electrons sliding off the end of a 
negative wire can not charge the electroscope, but if we 
provide a nice waiting room, like a condenser plate, 
then the electrons accumulate in this plate and enough 
collect to charge the electroscope. 

The Source of the Current.—The charge on the 
negative terminal sends electrons out into the wire at¬ 
tached to it. As fast as they move away, the charge 
of the terminal disappears. If you used a Leyden jar 
as in Experiment 15, there would be one rush of elec¬ 
trons and the flow would cease until the jar was re¬ 
charged. A dry cell acts in exactly the same way. Each 
bunch of electrons leaving the negative terminal dis¬ 
charge this terminal, and if it were not for the chemical 
action within the cell continually recharging the ter¬ 
minal, the flow of electrons would cease. This tells 
us how to define a cell. 

Definition of a Cell.—A cell is a device in which 
chemicals are used to continually maintain (keep up) 


PORTABLE SOURCES OF CURRENT ioi 


the potential (charge) of one terminal while keeping 
the other terminal either neutral or charged oppositely. 

A Bit of History. —In 1786 Galvani observed that 
when copper and zinc were held in contact like an 
inverted V and touched to the leg of a frog, that elec¬ 
tricity was produced. He thus produced electricity by 
chemicals. It was not until 1800 that Volta made a 
true chemical cell. 

Volta’s cell consisted of two strips, one of copper 
and the other of zinc, standing in diluted sulphuric acid. 
Their dry ends touched, but their wet ends were sep¬ 
arated. When the dry ends were held apart and were 
electrically connected by a wire, a current flowed in 
the wire. This simple cell is called by some the galvanic 
cell and by others the voltaic cell. 

Why a Cell Gives Out Energy. —Energy from 
the heat of the sun and from its ultra violet rays has 
been locked up in the minerals of the earth. When 
this energy is released in the chemical actions of a cell 
it spends itself in pushing electrons. 

Notice that I say when released in the chemical ac¬ 
tions of a cell. There is electricity in everything, but 
the hard job is to get it out and to get it out in such 
a way that we can catch it. 

Suppose you throw a few shovelfuls of fine damp 
coal into the fire box of your furnace and forget to 
close the door. The result that you get is not the fault 
of the coal. It was full of heat units and you gave 
them a chance to get out, but not in the proper manner. 
Hence they failed to heat the house. What a difference 
there would have been if everything had been just right. 

So it is with electricity. We must treat the materials 
correctly else the power produced may not be worth 
the money we have spent. 

One pound of zinc dissolved in sulphuric acid will 
give out 1026 British thermal units of heat but no elec¬ 
tricity. In a cell we might get 26 units of heat and the 


102 THE BOYS’ BOOK OF ELECTRICITY 


1000 units not as heat but as electrical energy. If 
everything worked perfectly, one pound of zinc should 
give 1/100 of a horse power for 100 hours. 

How Cells Push Electrons. —Suppose we make, 
operate, and then talk over, the action of a very simple 
cell. To prepare this cell we proceed as follows: 

Making a Simple Cell. —Experiment 20.—Place 
a glass nearly full of cold water in a basin, for what 
we are about to do may crack the glass and spill a 
corrosive liquid. In a test tube pour a teaspoonful of 
water. Slip a rubber band around the tube to mark the 
height of the liquid. Empty the tube and dry the inside 
fairly well; at least shake out all the water that you 
possibly can. Pour some concentrated sulphuric acid 
or oil of vitriol, as it is also called, into the tube up to 
the marker. Slowly pour this teaspoonful of acid into 
the glass of water. Stir slowly, but well, with a glass 
rod. Be careful to rinse the test tube well before laying 
It down. 

Never pour water into sulphuric acid, as it may get 
so hot that it will bubble violently and spatter acid on 
your skin or clothing. When this mixture of acid and 
water is cool, and not until then, may you put in the 
electrodes. 

To a strip of copper of convenient size for your 
glass—it can not be too big—solder a copper wire, or 
a binding post, if you have one. 

Prepare a rod of zinc in the same way. Sheet zinc 
is poor stuff for a cell, as it is eaten up so quickly. 

Place the zinc and the copper in the glass of acid and 
connect the wires to the galvanoscope with its resistance 
coil in series. The hook-up is given in Fig. 9. 

This cell is pulling electrons out of something and 
pushing them out on the wire connected to the zinc rod. 


PORTABLE SOURCES OF CURRENT 103 


How can a cell push electrons? To answer that we 
must consider what is going on inside of the cell. 

The Actions Inside of a Cell. —When you poured 
the sulphuric acid into the water a chemist would have 
said that you were ionizing the hydrogen sulphate. 






Fig. 24. When Sulphuric Acid is Poured into Water. 

You will get a better idea of what this means by an 
examination of Fig. 24 than if I wrote three pages 
about it. The illustration shows what happens when 
molecules of sulphuric acid fall into water and become 
ionized, each molecule of sulphuric acid forming three 
ions, two of hydrogen and one of sulphate. 













104 THE BOYS’ BOOK OF ELECTRICITY 

Sulphuric acid is a combination of two atoms of 
hydrogen and one radical of sulphate. The sulphate 
part is not a molecule nor an atom; it is a group of 
atoms which stick closely together. For all ordinary 
chemical actions a radical is inseparable. 

In a molecule of sulphuric acid the two hydrogens 
and the sulphate are held together by two electrons 
which act as links. The two hydrogen atoms are feel¬ 
ing, each separately, of course, “That electron is in 
my outer shell. If it were not for that electron I 
would have a "gone’ feeling in the outer layer of 
myself. Whenever I feel that way I develop most 
positive qualities. I really feel to the extent of one whole 
positive charge. I agonize over the situation, but those 
unfeeling scientists say I am ionised . But, thank good¬ 
ness, there is that electron and I feel quite neutral and 
happy.” 

Now, the humor of the situation is that the sulphate 
is also having a little talk with itself. 

# Most of the weight of these atoms and radicals is 
situated in the nucleus of each atom. Since these atoms 
do wonderful things, I shall assume that the brains of 
an atom is in its heaviest part, its nucleus. 

So the nuclei (plural of nucleus) of the sulphate are 
having a little chat. “Thank our lucky stars! If it 
were not for those two hydrogen atoms taking some 
of the responsibility of those two electrons on their 
shoulders we would still be in a frightfully negative 
condition. It is such a responsibility, hanging on to 
two electrons, more than we really care for. Oh, yes, 
of course we like electrons; we are very fond of elec¬ 
trons, but you know those two extra ones were such 
a care. They made us so negative. Nervous? No. 

I said negative, but after all, with two extra electrons 
why should we not feel nervous ? When we have them 
exclusively to ourselves, the scientists say ‘That sul¬ 
phate is ionized/ Perhaps they are right; certainly we 


PORTABLE SOURCES OF CURRENT 105 


know that we feel very negative. But now we feel 
quite neutral, for those two silly hydrogen atoms actually 
each think that one of those electrons belongs to it. 
Of course, those two electrons are a sort of common 
bond between us, the sulphate, and them, the two hydro¬ 
gens. You know, whenever we really get those two 
electrons all to ourselves, we can’t stand the nervous 
strain and we always hunt around and pick up some¬ 
thing that is fond of electrons and will play with them. 
No, no, I don’t mean just these special two electrons; 
all electrons look alike to us. As long as someone will 
play with two, any two, why sulphate is willing to form 
a company. The other fellow or fellows think they 
own the two electrons, so they are happy. We know 
we own them; that we can’t get completely rid of them, 
but we can feel quite neutral as long as any two of our 
electrons are not exclusively in our care.” 

All of these two musings of the hydrogen and the 
sulphate occurred in the bottle of sulphuric acid. As 
soon as you poured the hydrogen sulphate into the water 
there was a great commotion. There was the thirsty 
sulphuric acid combining with the water faster than 
you ever combined with a soda. This created the heat 
that you noticed. But that is not all. Most of the 
hydrogen sulphate was compelled to part company. The 
truly advantageous combination of hydrogen and sul¬ 
phate in which some two electrons kept both parts of 
the compound satisfied is now broken up. We say 
that the sulphuric acid is ionized. Take another look 
at Fig. 24. 

When the sulphate broke away it took two extra 
electrons with it and became negatively charged. The 
two hydrogen atoms each are short an electron and so 
each becomes positively charged. 

Electrolyte, Electrodes, Poles. —When an ionized 
solution is used as the liquid part of a cell it is called 
the electrolyte. When unlike materials are placed in an 


io6 THE BOYS' BOOK OF ELECTRICITY 


electrolyte these pieces of material are called electrodes. 
The dry ends of these electrodes are called the poles or 
the terminals of the cell. 

Another Definition of a Cell.—A cell is a com¬ 
bination of an electrolyte with two solid materials, one 
of which is dissolved by the electrolyte, while the other 
is not. 

Inside of the Cell Again. —Into your glass of 
sulphuric acid electrolyte place the zinc and the copper 
electrodes and connect the poles of this cell by a wire. 
It would be better yet to connect it to the galvanoscope 
as in Fig. 9. 

A Talk About Copper. —An atom of copper con¬ 
sists of a nucleus in which are closely packed 58 pro¬ 
tons and 29 electrons. Surrounding the nucleus are 
29 more electrons. When an enormous number of 
these atoms have been melted together and cast into a 
form, or electrically plated into a piece and then rolled 
into sheets or drawn into rods and wire, we have these 
atoms fairly close together. Not close, as you would 
figure closeness, but close for atoms. 

Pieces of metals have some of the electrons skipping 
from atom to atom and sometimes an electron tem¬ 
porarily belongs to two atoms. This leaves some elec¬ 
trons free. When a piece of copper is placed in an 
electrolyte which does not dissolve it, the copper is 
ready by means of its free electrons, to deliver electrons 
to any ion which needs them. 

Definition of an Ion .—An atom or group of atoms 
(radical) having an excess or a deficiency of electrons 
is called an ion . 

A Talk About Zinc. —What I have said about the 
copper in general applies to the zinc. The nucleus of 
zinc contains 60 protons and 30 electrons. There are 
30 electrons around the nucleus. 

. When zinc is placed in an electrolyte which dissolves 
it the zinc seems to take electrons from the ions of the 


PORTABLE SOURCES OF CURRENT 107 


electrolyte, and these, piling up on the zinc, produce 
such a crowd that they are pushed off and flow away 
in a electron stream along the wire attached to the zinc 
and copper poles. 

Thus the copper shoves off the electrons which it 
receives into the ions of the electrolyte and the zinc 



receives the electrons and pushes them out into the 
negative wire as electrical current. 

I know that I have not fully told why the cell fur¬ 
nishes current. 

There were many interesting and necessary details 
to be explained, but now I am ready for the explana¬ 
tion of why the chemical actions result in a flow of 
current. 

The Chemical Action in a Simple Cell is repre¬ 
sented at A in Fig. 25, which shows a glass jar with a 
strip of copper and a rod of zinc standing in an elec¬ 
trolyte of dilute sulphuric acid. 

























io8 THE BOYS’ BOOK OF ELECTRICITY 


Remember that the molecules of sulphuric acid which 
were electrically neutral when poured into water became 
hydrogen ions positively charged, and sulphate ions, 
negatively charged, because the sulphate stole two elec¬ 
trons as it was forced out of the sulphuric acid. The 
zinc electrode is composed of atoms of zinc, each of 
which has two electrons which are so far from the 
nucleus that they can get loose rather easily. From 
the surface of the zinc electrode, atoms are frequently 
darting out into the electrolyte. As they do this, they 
leave two electrons behind on the electrode. 

There are two important results from this action. 

When an atom of zinc hops off, leaving two of its 
electrons behind, it becomes positively charged. Hence 
the negatively charged sulphate ion and the positively 
charged zinc ion attract each other and would form 
actual molecules of zinc sulphate were it not for the 
water which keeps them separated. The electrons 
left on the zinc electrode are not needed by the atoms 
of zinc there. Each has its proper number of protons 
and electrons. These free electrons accumulate on the 
electrode until there are so many that they are crowded 
off on to the wire attached to it. 

This second action causes a flow of electrons away 
from the zinc pole of the cell, causing what we call 
a current of electricity. 

We must not forget the hydrogen ion—two of them, 
in fact—that came into the electrolyte along with each 
sulphate ion. These are positively charged. They are 
therefore repelled by the positively charged zinc ions 
which are around the zinc electrode. 

Probably each hydrogen ion wanders around until 
it gets near the copper electrode. This is composed of 
copper atoms having two electrons loosely attached. 
The hydrogen ions, being positively charged and hence 
looking for electrons, take the needed electrons from 
the copper atom of the electrode. This leaves the cop- 


PORTABLE SOURCES OF CURRENT 109 



u 

% 

I 

P-i 


VO 

d 

£ 







































no THE BOYS’ BOOK OF ELECTRICITY 


per electrode short of electrons. So it is now com¬ 
posed of atoms and ions and is in great need of 
electrons. 

If we now connect the wire from the zinc pole to 
the copper pole, then the electron forced out on this 
wire by the zinc electrode will flow around and be 
greedily ‘pulled out of the other end of the wire by the 
copper electrode. 

Thus you see the chemical action of the cell makes 
the zinc electrode a pusher of electrons. And the cop- 
per electrode becomes a puller of electrons, and so a 
steady stream of electrons flows through the connecting 
wire, and the cell furnishes an electric current. 

The action of this simple primary cell might stick 
in your mind better if you could get a vivid picture 
of what is going on in the cell. I am sure Fig. 26 
will help you to do this. 

In Lake Electrolyte there are two piles, one of cop¬ 
per, the other of zinc. Sam and Bill Hydrogen, twin 
brothers, have been swimming around with Miss Sul¬ 
phate and having a grand time. The Hydrogen twins 
have done the swimming and Miss Sulphate has been 
lazily floating. 

Seeing Ed Zinc, one of the atoms of zinc, for the 
Zincs are a large family, she calls, “Come on in; the 
water (acid) is fine.” Kicking off his two sneakers 
(electrons) Ed Zinc acquires two positive charges and 
diving into the water (acid) becomes an ion. 

Ed Zinc’s sneakers (electrons) race madly away on 
the plank (wire) and start to run around the margin 
of the lake (the circuit). They will ultimately reach 
the copper pile. 

As soon as Ed Zinc is in the water (acid) Miss Sul¬ 
phate devotes her time to him. Sam and Bill Hydrogen 
are as sore as wet pups. They swim to the copper 
pile, intending to put on sneakers, and sure enough 


PORTABLE SOURCES OF CURRENT m 


here are the sneakers galloping down the path (wire) 
to the copper pile. * 

Sam and Bill Hydrogen always were queer about 
sneakers (electrons) ; one for each of them seemed to 
give them perfect satisfaction. So the two of them 
will remove from the copper pile as many electrons as 
Ed Zinc started off from the zinc pile. 

A Practical Cell. —Such a cell as we have been 
talking about is not practical; in fact, no cell containing 
a liquid is a pleasant companion either in experimental 
work or practical everyday use. 

The cell shown in Fig. 25 B is called a dry cell. It 
consists of a zinc can, which acts as a container and 
also as the zinc electrode. In the center is a carbon 
rod. The electrolyte is damp instead of wet and sloppy. 
It is sealed with asphalt cement, and will work just as 
well standing on its head as if it were in its natural 
position. This cell will be fully described a little later 
on. 

The Ideal Cell. —Such a cell would have: 

1. Small resistance to the passage of electrons 
through it. 

2. A large force to push electrons at one pole and 
a large force to pull electrons at the other pole. 

3. The same pushing and pulling force for any 
electron stream. We would then have a cell which 
did not weaken under heavy work. 

4. The ability to produce electricity from cheap 
chemicals. 

5. No waste of chemicals. Every speck of the 
chemicals should produce electrons, pushing them out 
of the zinc pole and pulling them in at the copper pole. 

What the Simple Cell Will Not Do. —Since the 
simple cell does not have the qualities we have listed in 
the last paragraph, it would be well to find out what 
it will do and won't do. 

1 . It will not keep on pushing and pulling electrons 


ii2 THE BOYS' BOOK OF ELECTRICITY 


with the same vigor. It gets exhausted and requires 
a rest. 

2. It will not use chemicals economically. 

This means that there are two serious defects in the 
simple cell that we must remedy. We have found no 
material for the negative electrode as good as zinc un¬ 
less we pay a very high price. Considering quality and 
price together, zinc is the best for the negative electrode. 
Its price is high enough to make us very anxious to 
prevent waste. 

Local Action. —This is the name applied to the 
chemical action by which zinc is wasted. You will 
understand what happens and how it happens better 
if you try an experiment. 

Experiment 21.—Prepare a simple cell and connect 
its terminals by a piece of wire about six feet long. 
Watch the action of the zinc. Notice that it dissolves 
much faster at some places than at others. You may 
judge the speed of dissolving by the amount of bub¬ 
bling. Chemically pure zinc will show no bubbles. 

Zinc of the ordinary commercial grade of purity 
contains little particles of iron and carbon. These, with 
the zinc in which they are embedded, form little local 
cells in which there is a flow of electrons. Since these 
electrons never get into the wire connecting the poles 
of the cell they can not be made to work for us. The 
zinc is eaten up to* no useful purpose. 

Could we coat the zinc with a paint that would cover 
the iron and carbon pieces, protecting them from the 
acid, yet which would permit the zinc to pass through 
it to the acid, our troubles would.be solved. 

Amalgamation. —Fortunately there is such a coat¬ 
ing. Forming such a coating and watching it work is 
the best way to test the value of amalgamating the 
zinc. 


PORTABLE SOURCES OF CURRENT 113 


Experiment 22.—Remove the zinc rod from the sim¬ 
ple cell. Place it in a shallow dish with a few drops 
of mercury. Using an old tooth brush or a rag tied 
on a stick, rub the mercury over the surface of the rod. 
It becomes shiny and silvery. Rub until every part of 
the surface is amalgamated. 

You may need another drop of mercury, but hard 
rubbing will spread it nicely. You have formed an 
amalgam of zinc and mercury and you have not affected 
the carbon and iron pieces. 

Set up the cell, using this amalgamated zinc. Now 
there are no bubbles on the zinc, and no zinc is wasted 
in local action. None? Well, not quite none. Before 
amalgamation perhaps half of the zinc might have been 
wasted, but now not more than 3 per cent will be dis¬ 
solved without furnishing us with current. 

An amalgam is a soft alloy of mercury and any other 
metal. Keep mercury away from your jewelry and 
money. This amalgam covers up the iron and carbon 
pieces with an acid-proof coating, yet the zinc passes 
through the soft amalgam and is dissolved by the acid. 

Experiment 23.—Connect your simple cell to the 
galvanometer in the hook-up of Fig. 9. Do not close 
the circuit until you are ready to make the observations. 
Just as you close the circuit notice the reading of the 
galvanometer. 

In a few minutes the reading will be less and soon 
the reading will drop so low that you will know the 
cell is not pushing in any electrons. The cell is 
polarized . 

With a sliver of wood, scrape off the bubbles adher¬ 
ing to the copper strip. Give the electrolyte a good 
stirring, and a glance at the galvanometer will show 
that the cell is on the job again. 


U4 THE BOYS’ BOOK OF ELECTRICITY 

Polarization. —When a cell, by its chemical action, 
makes the positive electrode too much like its negative 
electrode, chemically speaking of course, then the cell 
does not pump electrons with the pressure that it used 
to. This condition is called polarization and is caused 
by a coating of bubbles of hydrogen gas forming on 
the positive electrode. 

Polarization Cured .—Since it is the hydrogen which 
causes the polarization, let us get rid of the hydrogen 
by turning it into water. This can be done by adding 
sodium bichromate to the cell. This chemical, with 
its large store of oxygen, will oxidize the hydrogen to 
water. 

As soon as we do this, there is a continuous dissolv¬ 
ing of the zinc even when we are not using the cell. 
We remedy this by placing the copper in an inner jar 
of porous earthenware, like an unglazed flower pot. 
The bichromate solution may be poured in around the 
copper. 

The zinc is not eaten up wastefully now, but to our 
dismay, we would find the copper dissolving. This we 
avoid by the use of a carbon plate, which makes as 
good a cell as the copper and zinc arrangement. 

This bichromate cell, sometimes called the Fuller 
cell, avoids polarization but is not suitable for home 
use. The liquid in it is far too corrosive. 

The cell whose internal construction is shown in 
Fig. 25 B is safe to use, since it is sealed. The de¬ 
polarizer is a solid material, black oxide of manganese. 
Being a solid, it absorbs the hydrogen very slowly, but 
in time it turns to water. 

To find out how well it depolarizes, connect the cell 
up according to Fig. 10. Close the circuit and, keep¬ 
ing it closed, watch the reading of the galvanometer. 
The reading will diminish. The cell keeping a high 
reading for a longer time has the better depolarizing 
action. 


PORTABLE SOURCES OF CURRENT 115 


Polarization Prevented .—If a cell could be designed 
so that no hydrogen came near the copper electrode 
there would be no chance for polarization. 

The Crowfoot or Gravity Cell. —In this cell, 
shown in Fig. 27 A, the phemical action keeps the 
hydrogen away from the copper. 

To put the cell together, place the copper element at 
the bottom of the jar. Fill it three quarters full of 



SULPHATE OF 
Z/MC solution 


SULPHATE OF 

SOLUTION 


ELEMENT 


OF 

WTJUOL 


Zn 


Hz | 

II 

S0 4 

1 __ 

n 

; 

_ 1 

SO+ j 

L_j 


j Cu 

1 

1 

1 

1 

— 1 

i 

• 

• 

1 

• 

• 

J Cu 

}C4/* 1 | 


B 


Fig. 27 . The Crowfoot Cell. 


diluted sulphuric acid. One teaspoon of acid to 40 of 
water is correct. Use the test tube measure for the acid. 

Drop in some large clean lumps of copper sulphate or 
blue vitriol, as it is also called, so that they fall in 
between the leaves of the copper electrode. 

Hang the zinc electrode on the edge of the jar. Con¬ 
nect the wire, and put the pell to work. At first you 
























n6 THE BOYS' BOOK OF ELECTRICITY 


will find the cell weak, but use will improve it. Never 
permit the cell to stand idle. When you do not want 
to use it, connect it to a magnet coil or resistance of 
some kind. 

Its Chemical Action. —The zinc is dissolved by 
the sulphuric acid. The hydrogen thus liberated steals 
some sulphate from the copper sulphate solution. This 
frees the copper, which is plated on the copper electrode. 
In this action the zinc is dissolved and the copper is 
plated. The zinc disappears and the copper grows. 

Its Electrical Action. —As atoms of zinc leave 
the zinc electrode to join the sulphate, they leave two 
electrons behind. 

When the sulphuric acid was split, at the time you 
diluted it with water, the sulphate took two extra elec¬ 
trons, leaving the hydrogen with a lack of electrons. 
These hydrogen ions wander towards the copper plate, 
and passing through the copper sulphate, stop, look 
and think. They then sneak up behind a copper sul¬ 
phate and steal its sulphate from it. The stolen sul¬ 
phate, with its two electrons which it always takes when 
it leaves anything, gives the hydrogen a satisfied feeling. 

But there was a copper associated with the sulphate 
before the sulphate deserted the copper and went with 
the hydrogen. This copper had two electrons taken 
away from it by the sulphate. Hence the copper at¬ 
taches itself to the copper electrode and takes two elec¬ 
trons from it. 

In this way, the action of the cell is continually piling 
up electrons in the zinc electrode, where they are 
crowded out to do work. The cell is also taking elec¬ 
trons away from the copper electrode, thus giving it an 
ability to pull electrons in out of the wire attached to 
the copper pole. 

Throughout this action, no hydrogen gets near the 
copper electrode, where it would stop the electrical 
action and thus polarize the cell. 


PORTABLE SOURCES OF CURRENT 117 


Electromotive Force. —Electron-motive force 
would better describe what is meant by the term electro¬ 
motive force. Some cells create a greater pressure to 
move the electrons than others. These are said to have 
a high electromotive force. This is abbreviated as 
“e. m. f.,” and quite frequently written in capital letters 
as E. M. F. 

A cell that pushes well, but that is partly polarized, 
will have a low e. m. f. 

Voltage. —Electricians have agreed to use the term 
e. m. f. for the electron-motive force of a cell or dynamo 
when it is ready to deliver electrons but not doing it. 
A cell standing on your table before you close the cir¬ 
cuit, and hence before the electrons begin to flow, is in 
this condition. 

The electron-motive force developed while electrons 
are actually being moved is called the voltage. The 
abbreviation is “e.” or “v.” 

Potential Difference. —Electrons flow from one 
place of high pressure or high potential, as it is some¬ 
time expressed, to a place of lower pressure or 
potential. 

When an instrument called a voltmeter, which is a 
galvanoscope with a coil in series with it, is connected 
by two wires to two places where the pressure is dif¬ 
ferent, it shows the voltage. This means the pressure 
pushing electrons between these places. This is also 
the difference in potential between the places. These 
two terms mean the same thing. For this reason, elec¬ 
tricians speak of the voltage or the p. d., the latter being 
an abbreviation for potential difference or what is the 
same, difference of potential. 

E. M. F. of Cells. —The electron-pushing force of 
a cell depends on the materials used. Carbon and zinc 
make the best combination for a reasonable expenditure 
of money. 

Voltage of Cells. —Some of the e. m. f. of a gell 


n8 THE BOYS' BOOK OF ELECTRICITY 


is used up in transferring the electrons across its own 
electrolyte. What is left is the voltage of the cell. 

Expressed in a rather inaccurate but wonderfully 
helpful way, we might say that: the e. m. f. is the 
voltage when the cell is not furnishing current, and the 
voltage is the e. m. f. when the cell is furnishing current. 

Resistance of Cells. —Every cell offers some op¬ 
position to the passage of electrons. This resistance is 
lowered by using large electrodes, placing them near 
together, and using an electrolyte furnishing many ions 
for carrying electrons across it. 

Notice that the less the resistance, the nearer the 
voltage is to the e. m. f., because less pushing force is 
used up in the cell. 

Quantity of Electrons Obtained. —The current 
or flow of electrons from a cell depends upon how fast 
the zinc is dissolved, how much the flow is impeded by 
the resistance of the cell and what its voltage is. 

Please note that, primarily, the current depends on 
the weight of zinc dissolved per hour. It is this action 
that puts electrons on the negative pole of the cell. 

Batteries. —A group of cells connected in any 
proper way is called a battery. A radio A battery is 
usually composed of three storage cells in one box. A 
bell ringer battery consists of several dry cells in a case. 
The radio B battery is a group of 15 small dry cells 
in one casing sealed up in a cement, so that only the 
terminals of a few of the cells show. 

Types of Cells.—Since cells are used for so many 
different kinds of work, it is natural that certain types 
have been developed and improved for a definite kind 
of job. 

High Voltage Cells. —The storage cell is the best. 
The average voltage is 2 volts. The bichromate cell 
will give 1.8 volts. 

Low Voltage Cells. —While this is not a desirable 
feature, it is well to know that the Crowfoot and 


PORTABLE SOURCES OF CURRENT 119 

Lalande cells are poor pushers. Their other very desir¬ 
able qualities make us overlook the 1 volt pressure of the 
Crowfoot cell and the 0.7 volt pressure of the Edison 
type, Lalande cell. 

Large Current Cells. —The storage cell and the 
bichromate cell lead in the large current, high voltage 
class. The Edison-Lalande cell furnishes more current 
at low cost of upkeep (replenishment and repairs) than 
other types. Its voltage is low. 

I Low Current Cells. —Not a quality to desire, but 
;the Crowfoot cell won’t furnish a large current, and 
we like it just the same. The reason will appear very 
shortly. 

! Wet Cells. —A most annoying feature of all cells 
but the dry cell is the corrosive liquid which forms the 
electrolyte. 

1 Clothing, floors and rugs will be ruined by contact 
with the chemicals in these cells. 

Dry Cells. —The cell shown in Fig. 25 B contains 
no liquid to slop around. A zinc can is the negative 
electrode. The electrolyte is a paste of sawdust, gelatin, 
ammonium chloride, zinc chloride and plaster, with 
enough water to make it moist. The better, and more 
* expensive cells, have zinc oxide in the paste. 

Around the carbon plate the paste contains black 
oxide of manganese. This turns the hydrogen liberated 
by the cell’s chemical action into water. 

The cell is sealed with a cement to prevent evapora¬ 
tion of the liquid and make the interior of the cell dry. 

A good dry cell is indeed a good cell. Of moderate 
voltage, about 1.5 volts, it will furnish a moderate cur¬ 
rent, polarizes slowly, recuperates rapidly, and its re¬ 
sistance is so low that it wastes very little of its e. m. f. 
inside of itself. 

Open Circuit Cells. —All the cells except the Dan¬ 
iel and the Crowfoot give better results on intermittent 
work. Any of them may be used for an hour or two, 


120 THE BOYS' BOOK OF ELECTRICITY 


but need a long rest after use in order that they may 
thoroughly depolarize themselves. 

None of these cells would operate steadily for a whole 
night of twelve hours without being a badly used up 
cell the next morning. 

Open circuit cells are those which work best and last 
longer without repairs, when the current is taken from 
them at intervals with rather long rests between. 

Closed Circuit Cells. —When a burglar alarm or 
a signaling device must be supplied with current for 12 
to 24 hours per day, we use Daniel on Crowfoot cells. 
These two are really the same cell, except that the 
Daniel, which has a porous cup to separate the liquids, 
is going rapidly out of use. 

Not only will the Crowfoot pell work 24 hours a 
day, but you must draw current from it all the time. 
If you let it stand idle, furnishing no current, you will 
have trouble. The blue solution of copper sulphate will 
rise, and when it touches the zinc it will copper plate it 
You then have two copper plates in the cell; it is 
polarized and will not push electrons. 

When used on a burglar alarm the battery is, during 
the day, switched over to another circuit. This circuit 
is a coil of wire of such conductivity that a small cur¬ 
rent will flow, not enough to use up much zinc, yet 
enough to keep the blue copper sulphate at the bottom. 

Primary Cells. —The cells which I have been de¬ 
scribing are called primary cells. When the zinc is 
consumed, a new one is purchased and placed in the 
cell. When from long use the cell is dirty from impuri¬ 
ties in the chemicals and dust which has fallen into it, 
the pressure may keep up but the zinc is now used 
wastefully. You do not get as many electrons per 
second as when the cell was new. 

The cell must be taken apart, the electrolyte thrown 
away, jar washed out, new electrolyte put in, the car¬ 
bon boiled in water and returned to the cell, the zinc 


PORTABLE SOURCES OF CURRENT 121 


amalgamated, and the cell with the zinc in place is again 
ready for service. 

Secondary Cells. —There is another type of cell 
called a storage cell, sometimes referred to as a sec¬ 
ondary cell. These cells are charged with chemicals 
and an electrolyte by their manufacturers. They fur¬ 
nish current, but like the primary cells their chemicals 
become exhausted. Since there is not zinc electrode in 
these cells, the negative electrode does not disappear. 
It changes, however, to a new and useless chemical. 

When such a cell becomes weak we do not buy new 
chemicals and make the cell over again. Passing a 
current of electrons through the cell reforms the chem¬ 
icals to what they were before. 

Do not make the mistake of thinking that current is 
stored up for future use. The current makes chem¬ 
icals which will go into action and produce a flow of 
electrons, just as in a primary cell. 

Storage Cells. —The common term for such cells 
is a storage battery. One cell has such a low pressure 
that we use them in groups to get pressures of 6, 12, 
32 or 110 volts, depending, of course, on the character 
of the job for which they are used. 

The Lead-Acid Cell. —This type of storage cell, 
which is usually called the lead storage cell, is the kind 
used in electric trucks for power and in automobiles 
for starting the motor and operating the lights. It is 
also used in the private electric light plants now so fre¬ 
quently used in country homes. The action will be 
best understood after doing an experiment. 

Experiment 24.—In a small jar mix sulphuric acid 
with five times as much water by pouring the acid into 
the water. Cut two plates of lead half as wide and as 
high as the jar. Solder wires or binding posts to them. 

Soldering to lead requires that the soldering copper 
be just hot enough to melt the solder. Scrape the lead 
until it is bright and use rosin for the flux. 


122 THE BOYS' BOOK OF ELECTRICITY 


Should lead plates be hard to obtain, use lead pipe, 
sawing off pieces as long as the height of the jar. 

Place the lead pieces in the jar of diluted sulphuric 
acid very close together. Should they be difficult to 
keep apart, place between them a sliver of wood. 

Using Fig. 28 as a guide, connect the cell just made, 
C, with the galvanoscope and its shunt G, a switch S, 



three or four dry cells in series, B, and by a wire back 
to other pole of C. 

The portion of the circuit that contains the push but¬ 
ton P and the electric bell A can be soldered to the 
wires already in use or clipped on by the clips sold by 
radio dealers. 

Right here we must come to an understanding about 
which way the current flows. All the books published 
up to date talk about the current flowing from the 
positive to the negative poles. 

The authors of these books know that the electrons 
flow from the negative to the positive pole. They are 
often very careful to tell you that our usual way of 
talking is wrong, but that folks have become so used to 
that way that changing is scarcely worth while. 



























PORTABLE SOURCES OF CURRENT 123 


I agree with this. Probably for another ten years 
we will be talking about the current flowing a certain 
way yet knowing that the electrons flow in the opposite 
direction. 

Whenever I say the current flows I shall mean in a 
direction opposite to the flow of electrons. When I say 
the flow of electrons is in a certain direction I shall 
be telling the exact truth. 

During a certain transition period you will hear me 
and others say that the current flows out of the positive 
pole of a cell and that the electrons flow out of the 
negative pole. 

For the remainder of the book watch sharply to see 
whether I say current or electrons before deciding that 
I have made an error in my explanations or our pictures. 

Experiment 24 Continued .—Close the switch S. If 
you have no switch use a push button and lay a heavy 
book on it to keep it down. The electrons which leave 
the negative pole of the battery B enter the cell C and 
find both lead plates have a thin coating of lead sul¬ 
phate on them. They naturally would, since they have 
been standing in sulphuric acid. 

At the electrode where the electrons enter the electro¬ 
lyte (the sulphuric acid), they cause the sulphate to 
enter the electrolyte. This leaves an electrode of pure 
lead. The sulphate entering the electrolyte splits the 
water there, taking the hydrogen to form sulphuric acid. 
The oxygen from the water goes to the other electrode 
and forms oxide of lead. This is a chocolate colored 
chemical. 

The passage of electrons through the cell has done 
chemical work and the results are: 

1. An electrode of pure lead. 

2. More sulphuric acid in the electrolyte than when 
the electrons started to pass through it. 

3. An electrode of lead oxide. 


124 THE BOYS' BOOK OF ELECTRICITY 

Chemists would call it peroxide of lead, for there 
are several oxides, each having a different color. 

After five minutes of charging the cell, open the 
switch S. The storage cell has now a lot of electrons 
sitting on the lead plate, because as soon as you stopped 
charging, there stood a primary cell, made by elec¬ 
tricity, but a primary cell just the same. 

Press down on the push button P, and the bell A 
will ring. The cell C will drive out the electrons and 
keep up the pressure to drive them until its active 
chemicals are exhausted. 

I really should say, until both plates are turned into 
lead sulphate. Since two materials of the same kind 
will not form a cell, two plates of lead sulphate or 
covered with lead sulphate, are worthless as electron 
pushers. 

Repeat this experiment, watching the indications of 
the galvanometer. While charging, the current went 
one way, and during the discharge, while ringing the 
bell, it went in the opposite way. 

For this reason, to charge a cell we connect the posi¬ 
tive pole of our supply to what will be the positive pole 
of the storage cell. 

The jar of a storage cell is usually made of com¬ 
position, hard rubber, or specially treated wood. Fig. 
29 shows a glass jar, which is sometimes used. This 
single cell has two negative plates with a positive plate 
between. This cell has a low capacity. More capacity 
is gained by using more positive plates, alternating with 
negative plates. 

The last positive plate has an extra negative plate 
placed beside it. The first and last plates are always 
negative plates. Positive plates charged on one side 
only are apt to bend and thus loosen the chemicals 
deposited on them. 

The Practical Lead Cell.—T he cell of Fig. 29, 


PORTABLE SOURCES OF CURRENT 125 


with perhaps larger plates and surely more plates, has 
cedar wood insulating sheets between the plates. These 
separators prevent the chemicals falling out of one 
plate from touching the other. They are porous, so 
that the acid soaks through, and electrons move through 



them freely. The positive plate is chocolate colored 
and the negative plate grey. 

The Alkaline Cell.—A cell perfected by Edison 
consists of nickel plated steel plates that are merely 
supports for the electrodes. These are formed in little 
cages of nickel steel, perforated to allow the electrolyte 
to penetrate the materials. 

The negative electrode is pure iron, and the positive 
electrode is nickel peroxide. The electrolyte is a 20 
per cent solution of caustic potash. 

This type of cell will stand much rougher electrical 
treatment than a lead cell. For the same capacity for 
work the Edison cell is half as heavy as the lead cell. 












126 THE BOYS' BOOK OF ELECTRICITY 


Using Storage Cells. —Lead cells should be re¬ 
newed by sending current into them until each has an 
e. m. f. of 2volts. You may use them until the 
pressure of each cell has fallen to 1volts. You must 
not use them any longer, as injury to the plates results. 
Over charging too much and too frequently injures the 
plates. Discharging to a completely empty condition 
also injures the plates. 

Follow the directions which come with a storage 
battery and it will give you good service. Remember 
that the denser the acid by a hydrometer test, the greater 
the charge in the cell. 

An Edison cell is charged up to a pressure of V/z 
volts. It can be charged and discharged at almost any 
rate. A lead battery must be charged and discharged 
at rates not greater than those given in the instructions 
which come with the battery. 

Sizes of Batteries. —A battery is made up of cells, 
usually made up in a block with but two terminals 
showing. A lead type 6 volt battery contains 3 cells. 

Each of these cells contains enough plates so that the 
energy stored up may be sufficient to send a current 
of so many amperes for so many hours. 

A 60 ampere-hour battery will furnish 6 amperes for 
10 hours or 3 amperes for 20 hours. I am quite sure 
that 12 amperes for 5 hours would injure the plates 
chemically and also buckle or bend them, due to severe 
and unequal heating. 

An ampere-hour is one ampere for one hour, or its 
equivalent. 

A 3 tube radio set may draw 3 amperes from the 
battery. Used for 2 hours it is using 6 ampere-hours. 
At this rate a 60 ampere-hour battery would last 20 
hours, after which it would be polarized and need 
recharging. 


CHAPTER VII 


MEASURING ELECTRICITY 

Need for Measuring 
The Electron 
The Coulomb 
The Ampere 
The Ohm 
The Volt 
The Farad 
The Henry 
The Watt 
The Kilo-Watt 
The Kilo-Watt Hour 
Computations 
Circuits 

A Dead Circuit 
A Live Circuit 
The Ground 
A Series Circuit 
Shunts 

Short Circuits 
Parallel Circuits 
Series Parallel Circuits 
The Flow oe Current 
Power 

The Water Analogy 
The Electrical Circuit 
Balky Cells 

The Importance oe Ohm’s Law 
Ohm’s Law 
Problems 
Divided Circuits 

Combined Resistance 
Rules for Computations 
Problems 
An Old Error 

Currents in Divided Circuits 
Experiment 25 

127 


128 THE BOYS' BOOK OF ELECTRICITY 


Joules Law 
I Square R 
Problem 

Why Big Wires 
Why High Voltage 
Drop 

Behavior oe A. C. 

The Three Wire Circuit 
A Model Electric Lighting Circuit 
Experiment 26 

A Two Wire Circuit 
Experiment 27 

A Three Wire Circuit 
In Your House 
Experiment 28 
no Volt Control Panel 
The Hook-Up 
The Lay-Out 
The Set-Up 
Its Operation 
Polarity Indicator 
Experiment 29 

Don’ts eor iio Volt Circuits 


CHAPTER VII 


MEASURING ELECTRICITY 

Need for Measuring. —Electricity could not be 
sold without definite units of quantity. Since work is 
accomplished by the quantity of electrons arriving at 
the job, but is accomplished the more quickly the faster 
these electrons arrive, we also need a unit combining 
these two factors. 

We need a unit for the pressure with which electrons 
arrive at the place where they do work. 

Since electrons are sometimes temporarily stored up 
in condensers, we need a unit for the capacity of things. 
Remember that we cannot store amperes, for they are 
electrons in motion. 

I have not discussed these units yet, because one can 
do a lot with electricity without measurements. How¬ 
ever, it is time that you know what these units are 
and their names, even though you do not personally 
intend to measure anything electrical. 

The Electron. —This is the tiny speck of negative 
electricity that measures all charges and currents. 
When an electron passes through a place it does some 
kind of work. It may heat, give magnetism, cause 
light, electro plate metals, dissolve metals, or it may 
itself take a flying leap from its conductor. 

We have selected a certain kind of work to deter¬ 
mine the number of electrons working on a job. When¬ 
ever, in an electroplating bath of silver nitrate solution, 
we find that 0.001118 grams of pure silver have been 
plated, we say one coulomb of electricity has passed. 

The Coulomb. —We use the word coulomb as an 
129 


130 THE BOYS' BOOK OF ELECTRICITY 


abbreviation for 6,300,000,000,000,000,000 electrons. 
While the electron is the actual unit, the coulomb is the 
practical unit. In the same way a stalk of asparagus is 
the actual unit of eating, but a bunch is the convenient 
unit in purchasing. 

The Ampere. —The more coulombs arriving each 
second, the sooner we will get our work done. If we 
had one word for a coulomb per second we could talk 
with greater brevity. We borrowed a word for this, 
taking a scientist's name. The ampere is that flow of 
electrons which amounts to 1 coulomb passing a point 
in the circuit every second. It was named after Andre 
Ampere. 

The practical method of determining an ampere is by 
use of a silver plating bath. When 0.001118 grams of 
silver are plated per second, then a current of one 
ampere is flowing. 

To find the current in a circuit a silver plating bath 
is inserted in the circuit so that the current will flow 
through it. The current is allowed to flow. Then 
the weight of the silver plating on the negative wire, 
divided by the number of seconds that the current 
flowed, and also divided by 0.001118 will give the cur¬ 
rent in amperes. 

You are perhaps thinking that this is a very difficult 
and tedious operation. Yes this is true, but we do not 
know of any method that is as accurate. 

If you will consider the following experiment you 
will understand the situation, and have a keener realiza¬ 
tion of the difficulty in getting an accurate measure for 
current. When I say an accurate measure, I mean also 
some effect that increases regularly as the current in¬ 
creases. 

Suppose as in Fig. 30 we had a circuit in which 
were a galvanoscope, an electromagnet, a silver plating 
bath, a lamp and a heater. The heater will be placed 
in a box, which will be surrounded by water. A 


MEASURING ELECTRICITY 


131 

thermometer in the water will indicate the temperature 
caused by the heater. 

Connect this circuit to a source of power and when 
the current is flowing you will observe that: the 
needle of the galvanoscope is deflected, the electro¬ 
magnet will support weight, the silver will be plated on 
the negative wire of the plating bath, the lamp gives 



light, and the thermometer shows that the temperature 
of the heater is increased. 

We now must observe closely the size of the different 
effects when the current is changed to twice and then 
three times its original value. 

The galvanoscope gives deflections of 2, 3 and 3.4 
scale divisions. Hence equal increases in the current 
do not give equal increases in the deflection. 

The electromagnet supports 9 lbs. then 11 lbs. and 
finally 11.5 lbs. So the strength of a magnet does not 
increase in the same proportion as the current. 

In the plating bath there is deposited; at first 4.025 


























132 THE BOYS’ BOOK OF ELECTRICITY 


grams per hour, then 8.05 grams per hour and finally 
12.075 grams per hour. Here we have an effect that 
is exactly in proportion to the size of the current. 

Let us see if the two remaining effects may be of 
value for measuring current. We are disappointed. 

The lamp is worthless as a method of measurement. 
At first the increase in light was startling and then 
the filament burnt up. 

The heater at first caused the thermometer to rise 
at rate of 1/10 of a degree a second, then at 4/10 de¬ 
grees a second and finally at the rate of 9/10 degrees 
per second. 

Looking over the effects of increasing the current to 
twice and then three times its original value, as shown 
by these instruments, you see that only the plating bath 
gave a regular and simple indication. 

The electro plating effect is equal for equal increases 
of current whether this is the first increase or the last 
of many increases. 

This is one reason the plating bath is the scientist’s 
instrument for the accurate measurement of current. 

The second is, that we may obtain balances, perhaps 
you would call them scales, that will weigh the ten 
thousandth part of a gram. Hence the silver deposited 
may be weighed with great accuracy. 

The Ohm. —Every material offers some opposition 
to the passage of electrons through it. We need a 
certain piece of material as a standard resistor and a 
name for it. 

A column of pure mercury 106.3 centimeters long, 
enclosed in a glass tube of 1 square millimeter inside 
area, is placed in melting ice. The resistance of this 
to the passage of electricity is called an ohm. This 
unit was named after George Ohm. 

Since the resistance of a material changes with the 
temperature, unless a particular temperature is stated 
we have an indefinite unit. 


MEASURING ELECTRICITY 


133 


The temperature of melting ice is easy to obtain 
and is always the same. Hence it was adopted for this 
and for many scientific standards, as the temperature 
at which the measurement is to be made. 

The Volt. —There must be a unit of electron-push¬ 
ing power, that is of e. m. f. What we call voltage 
will be measured by this unit. The pressure which will 
cause one ampere of current to flow through one ohm 
of resistance is called a volt. This unit is named after 
Alessandro Volta. 

The Farad. —Condensers really hold electrons or 
big groups of electrons called coulombs. If a con¬ 
denser could hold one coulomb when the tendency of 
the electrons to jump through the insulation is just 
one volt, then we say the capacity would be one farad. 
This unit named after Michael Faraday is so large that 
a micro-farad (one millionth of a farad) is our every 
day unit. Electricians call them “mikes.” So now 
you know what a “one mike condenser” means. Also 
that directions to buy a “triple oh five condenser,” 
really means to buy a condenser with a capacity of 
.0005 micro-farads. 

The Henry. —When the current in a coil of wire 
is increasing or decreasing, the coil resists the change. 
The coil is conservative, dislikes any change in the 
current through its wires, and produces an e. m. f. 
trying to stop this change. We say a coil has induc¬ 
tance. 

When an increase of the current by one ampere in 
one second causes the coil to develop a 1 volt pressure 
trying to stop us, we say the inductance of that coil is 
one henry. 

This unit was named after Joseph Henry of Albany, 
N. Y., who discovered inductance in 1830. 

The Watt. —What we folks want is the necessary 
work done in the least possible time. Each electron 
will do a certain amount of work. High pressure or 


i 3 4 THE BOYS’ BOOK OF ELECTRICITY 


voltage behind the electrons does not increase their 
speed. This is fixed by nature at 186,000 miles per 
second. Heat, light, electricity and radio all travel at 
this same speed. The voltage does increase the num¬ 
ber of electrons arriving. It also gives them a pushing 
and shoving ability. 

The work done depends on the amperes and the 
voltage, that is on the quantity of electrons per second 
and their pushing power. Thus the unit for measuring 
power is a combination of one ampere at one volt 
pressure and is called a watt, named after James Watt. 

The Kilo-Watt. —A watt is large enough for many 
measurements. For example:—writing this by the il¬ 
lumination furnished by a 50 watt Mazda lamp, I get 
an idea of what 50 watts of power will do. 

In the last few months the Electric Company has 
been sending me so many amperes at 110 volts pressure 
that the word watt represents too small a unit. We 
then speak of kilo-watts, each of which equals 1,000 
watts. Kilo means 1000. 

The Kilo-Watt Hour. —You will agree that if the 
Electric Company serves me at the rate of one kilo¬ 
watt, they should be paid in proportion to the number 
of hours they do it. 

For this reason, the meters which determine our 
electric bills, register the result of three things 1— 
amperes, 2—volts, 3—time in hours. The combination 
of 10 amperes at 100 volts for 1 hour, or any com¬ 
bination amounting to the same ability to do work will 
be called a kilo-watt hour. 

Computations.—I think you will agree with me 
when I say that the ability to handle electricity intelli¬ 
gently, to make the front door bell ring again when it 
takes a vacation, to operate and perhaps make a radio 
set, is to be attained before you bother with problems 
in computation. 

The next thing will be to understand why the 


MEASURING ELECTRICITY 


i35 


familiar electrical things work. This is not a matter 
of arithmetic. It has to do with the nature of things, 
not their quantity. 

There are a few rules that you may wish to know 
about, but you must know more about circuits and 
what happens in them, before you tackle the rules. 

Circuits.—The path through which the electrons 
pass may include wire instruments, machinery, vacuum 
tubes, heaters and such devices. It is called a circuit 
because the electrons make a circuit back to their start¬ 
ing point. Line is a slang word for circuit. 

The word circuit is used with many others, and so 
we have series circuits, parallel circuits, shunt circuits, 
short circuits, etc. 

A Dead Circuit. —Before a switch has been closed 
to connect a circuit or line to the battery or the dynamo, 
there is no current in the circuit and we say that it is 
dead. 

A Live Circuit. —Suppose that in a power house a 
generator is running at full speed and that no wires 
are attached to its terminals. No current flows but the 
full pressure or e. m. f. is at the terminals. 

Wires may be attached to this generator and brought 
through the streets to your room ending there in an 
empty lamp socket. Pull the chain or push the switch 
or do whatever in your home would light the lamp if 
it were in the socket. 

Electrons will flow along the wire to this socket 
and there stop, for there is no complete path, there is 
a gap in the circuit. There is no current flowing now. 
There was at first a rush of electrons but when that 
was over there was no more movement of electrons. 

Such a circuit we call a live circuit. Should you 
remove both fuses from the house supply wires, then 
your wiring will be dead, but the wires in the street 
will be live. 

Beware of the open place or the gap between the 


136 THE BOYS’ BOOK OF ELECTRICITY 

wires of a live circuit. Should you bridge this gap 
with your body, or should you touch twc points near 
in feet but electrically, far from each other, you will 
receive a shock. This shock may be a mere trace of 
feeling, a tingle or a serious shock, depending upon 
the voltage applied to the line. A radio set, with four 
blocks of B batteries in series, will give you a shock 
that you will remember, provided that you touch the 
wrong places. Ninety volts have some kick to them, 
especially if your hands are damp. 

The Ground. —When one part of a circuit is com¬ 
posed of copper wire and the remainder of railway 


magnet RESISTANCE 



rails, water pipes, or the earth, we speak of the copper 
part as the line and of the remainder as the ground. 

Your radio set may be connected to the ground. This 
means that you are using the air and the ground as a 
means of leading the radio waves to your set. 

A Series Circuit. —An inspection of Fig. 31 will 
show that a series circuit is one in which the same 
electrons pass through every wire and device in the 
circuit. 

Starting at the source of power the wires go to a 
double pole switch. When this switch is open the 
circuit is dead. If a single pole switch were used one 
side of the circuit would be alive all the time. 

When the switch is closed the current flows through 
the magnet, the lamp, the resistance and the electro¬ 
plating bath, for they are all in series. 










MEASURING ELECTRICITY 


137 


In such a series circuit, the same current must pass 
through each piece of apparatus. The lamp requires 
1/3 of an ampere. The electro plating bath 10 or 
more amperes. It is evident that a series circuit is 
not adapted for serving different kinds of apparatus. 

Suppose all the lamps in a house were on a series 
circuit. When one lamp is to be turned out or shut 
off, the circuit must be opened. Then all the lamps 
go out. 

In series circuits we may divert nearly all the cur¬ 
rent around a certain place by using a jumper or a 
shunt. 

Shunts .—At y in Fig. 31 is shown two wires which 
when joined will carry some of the current around 
the resistance. If the resistance of the path through 
y is low, most of the current which before went through 
the resistance will now go through this new path. 

A low resistance path such as has just been described 
is called a shunt. 

The wires at x when connected make a shunt. But 
this kind of a shunt forms a path around all the re¬ 
sistance of the circuit. 

The laws of nature are such that a small resistance 
means a large current. Hence if the shunt at x is 
completed such a large current will flow as will over 
heat the wires, perhaps even melt the solder on the 
joints in the wires. 

Any path of low resistance, which causes a very 
large current to flow is called a short circuit. 

Short Circuits .—These are usually short in length 
and very low in resistance, causing dangerously large 
currents to flow. 

Keep metal tools away from circuits, lamp sockets 
and storage batteries. Never try to repair any electrical 
device unless it is removed from the source of power. 
Since lamp sockets can't be removed, before fussing 
with them, personally remove the fuses in that cir- 


138 THE BOYS’ BOOK OF ELECTRICITY 


cuit. Until you are quite expert, leave jobs on the 
house wiring to electricians. It is better to be safe 
than sorry. 

Parallel Circuits. —In order to bring the source 
of power to each device used and thus make them in¬ 
dependent of each other the hook up of Fig. 32 is 
used. 

In this arrangement each piece of apparatus may be 
connected or disconnected, without affecting the others. 
This is the arrangement of the lamps in our homes. 

A low resistance connected at x or anywhere on 
the circuit, as at y, produces a short circuit. Do not 



connect any device to the wiring of your home until 
you are sure that it will not cause a short circuit. 
Electrical toys and experiments should never be con¬ 
nected to the house wiring. Look at Fig. 6. Read the 
explanation of it. Then attach your experiments or 
toys to the proper safety device and attach that to the 
house wiring system. 

Series-Parallel Circuits. —When each part of a 
set of parallel circuits contains several pieces of appara¬ 
tus in series, we have a series-parallel combination. 

The lights of a trolley car are arranged in this way. 
In order to push the electrons the long distances the 
voltage applied to the trolley wire or the third rail 
must be larger than that used for house lighting. It is 
usual to have an e. m. f. at the power station of from 
550 to 750 volts. 

Suppose the average voltage in the cars of a trolley 








MEASURING ELECTRICITY 


139 


road to be 550 volts. If the same type of lamp is 
■used in these cars as is used in your home, then the 
550 volts would send through one of these lamps, de¬ 
signed for use at 110 volts pressure, a current 5 times 
as large as it was built to carry. The lamp would 


LAMPS JN AN ELECTRIC CAR 





Fig. 33. Series-Parallel Circuits. 

burn brilliantly for less than a minute and then the 
filament would melt. 

This could be avoided by making a special lamp, 
sturdy enough to stand up against the 550 volts, but 
this would be very expensive. 

If however, 5 lamps were arranged in series the set 
would be able to stand 550 volts. Now refer to Fig. 
33A and notice that each set of 5 lamps in series is 

















140 THE BOYS' BOOK OF ELECTRICITY 

connected to the feeding wires in parallel. In this way 
each set of 5 lamps is subjected to 550 volts, yet each 
set of lamps is independent of the others. 

Should any one of the 5 lamps of a set burn out, 
the whole set will go out. 

In many electric railway cars, over the doors and 
On the platforms, are lamps which only light when the 
trolley or third rail shoe gets out of contact with the 
feeder wire or rail These are operated by a storage 
battery and thrown into the circuit of that battery 
by an automatic switch. This switch is held open 
by a magnet operated by the current going to the 
motors. When this current fails, the magnet is demag¬ 
netized, the switch lever is allowed to fall, and the cir¬ 
cuit of the storage battery is closed. 

When the motors get current again, the switch lever 
is pulled up and the circuit broken. These lamps are 
special lamps designed to run on low pressure. 

Speaking of motors, reminds me that the two motors 
of an electric railway car are connected in series to 
start the car and to run it at low speed. When the 
car has attained the greatest possible speed with the 
series arrangement, then the two motors are connected 
in parallel. These connections are shown in Fig. 33 
at B and C. 

These changes are made by the controller. This is 
a rotating cylinder carrying switches which make, 
break and rearrange the circuits. 

As the motorman turns the handle the first move¬ 
ment arranges the motors as in Fig. 33B, then each 
of the motors receives half the voltage of the line 
and so they run at low speed. Thus the car is started 
without the wheels slipping. 

Subsequently the motors are connected in parallel 
as shown in Fig. 33C. Each motor now receives the 
full voltage of the line and they run at their highest 
speed. 


6 


a 


/o 


MEASURING ELECTRICITY 




141 


—< 7 > 


/vyW{7>—<7> 




A/\/\/\ -<(Y^i-(2 ) ■ — 




. 7 


/w^ r 0»-r r ^> 





Fig. 34 . Series-Parallel Control of Railway Motors. 











































142 THE BOYS' BOOK OF ELECTRICITY 


There is a resistance which is used to gradually in¬ 
crease the speed of the car. The way this resistance 
is connected into the circuits is shown in Fig. 34. 
You will see there how the resistance is cut out; how 
it is thrown in the circuit again as the motors are 
placed in parallel, and how again cut out to increase 
the speed of the car. 

There would be ten positions of the handle of the 
controller while starting the car. In motorman’s slang 
these positions are called notches. 

The Flow of Current.—Now that you are familiar 
with circuits, let us -consider how electricity flows 
through them. You know that certain devices pump 
up an electrical pressure. Have you noticed that the 
steam, pneumatic or hydraulic engineer is always 
worrying about the pressure. The indications of the 
pressure gauge are of the utmost interest and im¬ 
portance to him. Of course he does not like leaks, but 
not so much because they lose material as because 
they lose pressure. You see the steam, the air or the 
water would be of no use to him were they not de¬ 
livered under pressure. 

The electrical engineer wants a stream of electrons, 
but he wants them under pressure. In fact 5 million 
electrons will do the work of 10 million, if the smaller 
number are delivered at twice the pressure. 

Power. —Since it is the quantity of electrons ar¬ 
riving per second and the pressure behind them that 
tells us what power there is for our use, the electrical 
engineer also talks a lot about watts. 

A watt is not a thing that can be made by electrical 
cells or dynamos and sent out to the engineer. We 
must send amperes, with volts of pressure; the com¬ 
bination makes watts. 

The Water Analogy.—We can get a very clear 
idea of the flow of electricity by considering the flow 
of water in a pipe. 


MEASURING ELECTRICITY 


143 


When there is a current of water flowing, it is be¬ 
cause there is a high pressure at one place in the pipe 
and a lower pressure at some other place. To say it 
differently the current is caused by a difference in pres¬ 
sure. 

The current will be greater or less as this difference 
in pressure is greater or less, and this current will also 
depend upon the resistance offered by the pipe. If 
we desire to alter the current, we may open a faucet 



Fig. 35. A Simple Hydraulic Circuit. 


more, thus lessening the resistance. We may also get 
an increased flow by telephoning to the Water Com¬ 
pany and asking them to increase the pressure. 

The flow of water is controlled by the pressure and 
the resistance. 

The electrical engineer proceeds in the same way to 
find what pressure is available, and then he so alters 
his resistances as to cause the current he desires, to 
flow. 

To make the analogy between a water system and 
an electrical system we must make a closed circuit in 
each case. In Fig. 35 is shown a closed circuit in which 
















144 THE BOYS’ BOOK OF ELECTRICITY 


water circulates so that there is no waste of water, 
for the same water is used over and over again. 

The rotary pump takes in water from the tank, 
and gives the water a pressure so that it flows out with 
considerable force. The pressure gauge at the intake 
of the pump reads zero, but the gauge at the delivery 
pipe of the pump reads 110 lbs. per sq. in. This means 
that every square inch of any thing trying to oppose 
the water would feel a force of 110 pounds. 

To the faucet, which is wide open, is attached a 
water motor. This motor drives a grindstone. The 
outlet pipe of the water motor runs to the tank. 

Please remember that we are not generating water, 
we are simply putting the water which is already there 
into motion. The water meter will tell us the quantity 
of water which passes through the pipe to the motor. 

The readings of the two pressure gauges show us 
what pressure the pump is furnishing. The difference 
between the readings of the two pressure gauges shows 
the force that causes the water to circulate in the con¬ 
ducting path that we have provided for it. 

If a tightly fitting cover were put upon the tank 
and the water flowed from the motor with 10 lbs. per 
square inch pressure, then the pressure in the tank 
would be 10 lbs. per sq. in. 

Since the pump can add 110 lbs. per sq. in. pressure 
to the liquid entering its inlet, then the pump would 
deliver the water at 120 lbs. per sq. in. 

The difference in pressure would still be 110 lbs. 
per sq. in. and the motor would operate as well as it 
did before. 

Returning to the case where the tank is open, as 
shown in Fig. 35, suppose we partly close the faucet. 
This increase in the resistance of the circuit to the 
flow of water will result in a lessened flow unless the 
pump is driven at a higher speed. 

Pressing a knife upon the grindstone slackens the 


MEASURING ELECTRICITY 


145 


speed of the motor. Now if it was an electrical motor 
it would draw more electricity and fight hard to keep 
up its speed and power. The water motor does not. 
So although thinking of water or hydraulic circuits 
helps you to understand electrical circuits, thinking of 
water motors will not help you at all in understanding 
electrical motors. 

If we stop the pump the two pressure gauges will 
both read zero, and no work can be done. The same 



amount of water will be there as before, but being 
at rest cannot do work. 

Let us close the faucet and start the pump. Before, 
when the faucet was open the water could flow away 
from the pump. The pump had to push very hard 
on the water as it was flowing away in order to keep 
up a pressure of 110 lbs. per sq. in. Now the faucet 
is closed and the pump can, without working any 
harder, keep up a pressure of 120 lbs. per sq. in. at its 
delivery pipe. 

All these things are simple, and they are quite easily 
understood. Keeping in mind that an electrical cir¬ 
cuit has similar actions going on in it, we will now 
consider an electrical circuit. I am sure you will find 
that what happens in it may be readily and thoroughly 
grasped and tucked away in your brain for future use. 










146 THE BOYS’ BOOK OF ELECTRICITY 


The Electrical Circuit.—After a parting glance 
at the hydraulic circuit turn to Fig. 36. Here I have 
made a complete circuit of copper wires and appliances 
which conduct electricity. I could use the earth in the 
same way as I used the tank in Fig. 35 as a storage 
place. We seldom do this in electrical circuits be¬ 
cause the resistance of the earth is higher than that 
of copper. 

It costs less to operate a circuit such as shown in 
Fig. 36 than one using the earth either as a conductor 
or a storage tank. Hence if we have enough money 
to build what is called a complete metallic circuit we 
do so. Frequently it pays to borrow the money to 
build a complete metallic circuit, for we repay the 
borrowed money out of the savings, in the operating 
costs. 

In railroad work where years ago we used the earth 
as one conductor, we now use the regular train rails 
as the other conductor. We even go so far sometimes 
as to add to the conductivity of these train rails by 
running a copper wire in parallel with them. This 
means that the current has three metallic paths to fol¬ 
low on its trip back to the power house. 

Looking at Fig. 36, let us start at the generator. 
Whether of the a. c. or d. c. type, it is merely a device 
for pumping electrons just as the water pump acted 
on the water. The generator pumps electrons by 
maintaining a difference in pressure between its ter¬ 
minals. 

There are two wires attached to the circuit, one on 
each side of the generator. These wires lead the pres¬ 
sure at the spot where they are attached up to the 
voltmeter. The voltmeter reads the difference in pres¬ 
sure between these wires. 

A voltmeter reads the difference in pressure between 
the two points in the circuit to which it is attached. 

It seems as if the voltmeter actually subtracted the 


MEASURING ELECTRICITY 


147 


pressures and indicated the answer. Notice that one 
voltmeter does for the electrician what two pressure 
gauges did for the hydraulic engineer. 

We can get the pressure at a given place by use of 
an accurately constructed gold leaf electroscope, but 
we very seldom want this information. Since it is 
difference in pressure that causes electrons to flow 
we are glad that the voltmeter gives us this informa¬ 
tion directly. 

Perhaps you have been thinking from the time of 
your first glance at Fig. 36, that the wires to the volt¬ 
meter and the instrument itself formed a circuit which 
robbed the main circuit of current. 

It is true that the voltmeter circuit is a shunt and 
hence is in parallel with the main circuit. It draws 
away from the main circuit only about one hundredth 
of an ampere. Remember that a galvanometer to be 
used as a voltmeter must have a coil in series with it. 
We make the resistance of this series coil quite high. 
So little extra current is drawn by the voltmeter when 
connected to the circuit as a shunt, that in practical 
work we entirely disregard that current. 

The amount of current is measured by the ammeter 
so placed that all of the current leaving the source is 
measured by it. Yes, some of the current does go 
through the shunt, but the galvanometer and its shunt 
together make the ammeter and this instrument is 
marked to give a reading that tells you what current 
is in the circuit of which the ammeter is a part. 

The rheostat or variable resistance was placed in the 
circuit in order to regulate the flow of electrons, as 
the faucet regulated the flow of water. 

While the ohms of resistance in a rheostat do not 
change, the effect of the rheostat does change as you 
move the rheostat from one circuit to another. 

Once I was using a 10 ohm rheostat in a circuit with 
5 ohms of wire and apparatus. Changing this rheostat 


148 THE BOYS' BOOK OF ELECTRICITY 


from 0 ohms to 10 ohms made a great change in the 
current. As I remember the results, I found I could 
change the current from 2 amperes down to 2/3 of an 
ampere. 

A friend borrowed this rheostat and placed it in a 
circuit with a lamp. He wanted to make the lamp 
burn very dim and then bright. The lamp had a re¬ 
sistance of 330 ohms. The total resistance of the cir¬ 
cuit changed so little with this rheostat in the circuit 
that the electrons found very little extra opposition. 

When my friend returned the rheostat remarking 
that it was no good, that it scarcely changed the cur¬ 
rent, I told him that he had better learn Ohm's Law. 
In a few minutes that is just what we are going to 
do. 

Suppose the generator in Fig. 36 to be revolving at 
its proper speed. The voltmeter reads 110 volts. A 
flow of electrons takes place throughout the circuit. 
These electrons were there before the generator was 
in operation. The difference in pressure serves to push 
them around. 

If now we open the switch no current can flow and 
the volts that formerly pushed the electrons through 
the generator now are not used up in that way. The 
voltmeter now reads 120 volts. The e. m. f. in that 
circuit is 120 volts but the voltage on the circuit which 
we attached to the generator is 110 volts. 

Balky Cells. —We now see why cells having a 
high internal resistance may show up 1.5 volts when 
the voltmeter is attached to them, but when used in a 
circuit give less than 1 volt. 

Because some of the volts of a cell are always oc¬ 
cupied in chasing the electrons through the cell itself. 
The remaining volts push the electrons through your 
wires and apparatus. The larger the current the greater 
is the number of the volts of the e. m. f. of a cell 
used up in sending the current through the cell itself 


MEASURING ELECTRICITY 


149 


and the less left for sending the current through your 
toys and experiments. 

It is the volts that get used up in pushing electrons 
through the circuit. The number of electrons moving 
is the same at all parts of a simple circuit. 

The Importance of Ohm's Law. — One cannot 
use electricity much without wanting to know what 
current will flow when we do certain things. Often 
we must find out how many others will choke the cur¬ 
rent down to a certain number of amperes. 

Sometimes when a circuit is set up, we know how 
many amperes must flow to operate the apparatus, we 
know how many ohms of resistance the circuit opposes 
to the e. m. f., and we must calculate how many volts 
are needed to send the desired current. 

We can do all of these things by using Ohm's Law. 

Ohm's Law. —The current in amperes is equal to 
the difference in potential in volts divided by the re¬ 
sistance in ohms. 

As a formula— 

Volts 

Amperes =- 

Ohms 

as often expressed using letters, 
e 

r 

Problems .—A few problems will make the use of 
the law clear. 

I.—I have two dry cells and a 5 ohm telegraph 
sounder. If I connect all these in series with a key, 
what current will flow ? 

You have two cells each with e. m. f. of 1.5 volts. 
In series they will add their voltages, hence the total 
e. m. f, is 3 volts. 



150 THE BOYS’ BOOK OF ELECTRICITY 


The resistances opposing the flow of current are: 

1. The resistance of the cells. This is about 0.1 ohm 
for each cell or 0.2 for the two in series. 

2. The resistance of the wire used to connect the 
cells to the sounder. This is about 0.25 ohm. 

3. The resistance of the contacts where the wires 
are connected to the binding posts and of the moving 
contact in the switch or key. This may be as much as 
0.75 ohm. 

4. The resistance of the sounder, which is 5 ohms. 

All these resistances are in series and thus add their 

effects, making a total of 6.2 ohms. 

Using Ohm’s Law we find that the current in am¬ 
peres will be—3 volts divided by 6.2 ohms which is 
0.48 amperes. Thus we may expect a current of 
about an ampere to flow in this set up. 

II. —It required 5 dry cells in series to obtain a 
current of 2 amperes through the coil of an electro¬ 
magnet. What was the resistance of the magnet? 

The e. m. f. is 5 times 1.5 or 7.5 volts. The total 
resistance of the circuit is enough to make the current 
2 amperes. 

From Ohm’s Law we see that the volts divided by 
the amperes give the resistance of the circuit. Since 
7.5 volts divided by 2 amperes gives 3.75 ohms, the total 
resistance of the circuit is 3.75 ohms. But the cells 
offer about 5 x 0.1 ohm = 0.5 ohm, for they are in 
series. 

When the resistance of the cells themselves, 0.5 
ohm, is subtracted from the total resistance, 3.75 ohms, 
the result, 3.25 ohms is the resistance of the electro¬ 
magnet. 

III. —A 6 volt storage battery is connected to a radio 
receiving set using 4 amperes of current. The wires 
between them have a resistance of 0.2 ohm. What 
pressure will be delivered to the set? 

From Ohm’s Law we see that the volts required 


MEASURING ELECTRICITY 


I5i 

to push a current through a resistance may be found 
by multiplying the amperes by the ohms. 

Hence the voltage required to deliver the current to 
the set will be 4 X 0.2 = 0.8 volts. So the pressure at 
the set will be 6 — 0.8 = 5.2 volts. 

Before you leave this problem be sure that you under¬ 
stand that 0.8 volts was destroyed in pushing the elec¬ 
trons through the opposition offered by the 0.2 ohms 
resistance. 

Divided Circuits.—When a 6 ohm coil and a 
3 ohm magnet are connected in series the resistance is 9 
ohms. When connected in parallel so that the current 
splits and goes through both, the resistance that they 
offer is lowered. 

When two paths conduct the current the opposition 
is less than if there were only one. For this reason 
the effect of two resistances in parallel is to offer a 
resistance less than the resistance of the smaller of the 
two. 

To gain a clear idea of these facts, we will consider 
first a simple circuit, one that may be in your home 
today. 

A 110 volt supply from a generator serves a toaster 
which, offering 22 ohms resistance, has a current of 5 
amperes flowing through it. Please do not say “Cer¬ 
tainly, by Ohm's Law that is the current that must 
flow." Not at all. Since this voltage does send through 
this resistance 5 amperes by the laws of Nature, George 
Ohm could by patient investigation discover Nature’s 
law. This value of 5 amperes is not the result of Ohm’s 
Law, rather Ohm’s Law is the result of the actual facts. 

In Fig. 37 we have the hook-up of a circuit that may 
have been upon the breakfast table this morning. 

The generator furnishes a pressure which delivers a 
voltage, which means difference of pressure, in the 
lamp socket of 110 volts. The attachment plug leads 
this voltage to the toaster. The resistance of it I calcu- 


152 THE BOYS' BOOK OF ELECTRICITY 


lated by Ohm’s Law, for it bears a label saying that it 
takes a current of 5 amperes. 

This means of course that on an ordinary house 
lighting system it takes about 5 amperes. Ohm’s Law 



enables me to calculate that its resistance is about 22 
ohms. See Problem II on page 150. 

# The generator and the toaster form a simple series 
circuit. Every lamp socket and every socket for an 
attachment plug in the house is connected to the same 





















MEASURING ELECTRICITY 


153 


wires. If then you now attach a grill to another lamp 
socket, and this grill has 22 ohms resistance, it will take 
5 amperes also. This grill and its wires are shown in 
dotted lines in Fig. 37. You now know that connecting 
a second resistance of the same value as the first, in 
parallel with the first, doubles the value of the current 
taken from the generator. 

Let us consider these two appliances as a unit. Per¬ 
haps wiring them in a different way would make this 
clear. Suppose we brought, as shown in Fig. 38, one 
wire from the attachment plug, split this wire so as to 
carry current to each appliance; then brought the two 
outlet wires back into one, and took this wire back to 
the attachment plug. 

You would now have the same electrical condition as 
you had in Fig. 37 when the toaster and the grill were 
both connected to the chandelier. You have two 22 
ohm resistances in parallel, and the resistance of the 
combination is half that of one resistance. 

The effect is as if both the 22 ohm resistances were 
removed and one 11 ohm resistance were substituted. 
If you actually made that substitution a current of 10 
amperes would flow. 

This is a case where two equal resistances are in 
parallel. If the resistances of the appliances were un¬ 
equal, calculating the result would not have been so 
simple a matter. 

An actual experiment made with a 6 ohm and a 3 
ohm coil in parallel would show that they will allow a 
current of such a size to pass as indicates that the com¬ 
bination offers but 2 ohms resistance. 

Combined Resistance. —You need rules for find¬ 
ing the actual resistance offered by a combination of 
several resistances in parallel, or as we say, their com¬ 
bined resistance. 

There are two rules which will solve the problems 
arising from your experimental work. 


154 THE BOYS' BOOK OF ELECTRICITY 



Rules for Computations. — 1 . The effect of plac¬ 
ing a number of equal resistances in parallel is to add 
to the circuit a resistance equal to the resistance of one 
of them divided by the number of them. 

2. The effect of two resistances in parallel is to add 


















MEASURING ELECTRICITY 


155 


to the circuit a resistance equal to the product of their 
resistances divided by the sum of their resistances. 

Problem I .—Five lamps each of 330 ohms resistance 
are in parallel on a 110 volt circuit. What resistance 
do they offer to the passage of electrons? 

Since they are all equal, their combined resistance 
will be H of 330 ohms, which is 66 ohms. 

Problem II .—Two resistances of 9 and 3 ohms each 
are connected in parallel. What is their combined re¬ 
sistance ? 

They are unequal, hence the “product divided by the 
sum” rule applies. 9 X 3 = 27. 9 + 3 = 12. 27 -f- 
12 — 2.25 ohms. The combined resistance will be 2.25 
ohms. 

An Old Error.—How often have I been told 
that the current followed the path of least resistance, 
thus leading me to infer that no current would go 
through a high resistance path when it was paralleled 
or shunted by a low resistance. 

The truth of the matter came to me when I tried to 
induce current to leave a certain wire by placing low 
resistance shunts on that part of the circuit. Some cur¬ 
rent always flowed through the original wire. 

The current divides and goes through all the paths 
offered to it, each path carrying a current in proportion 
to its conductivity. 

Currents in Divided Circuits.—Suppose you have 
a small lamp, a resistance coil and a magnet, each of 
such a resistance that they will operate satisfactorily 
on a 2 volt supply. 

Suppose you wish to connect them so that any one of 
the three can be operated alone or two or all three may 
be in use at once. 

Experiment 25.—Take the device shown in Fig. 5 
and fasten three wires to each terminal of the switch. 
Using one pair of these wires, connect a small S. P. S. 


156 THE BOYS' BOOK OF ELECTRICITY 


T. (single pole, single throw) switch and the lamp in 
series. Using another pair of wires, hook up a S. P. 
S. T. switch and the resistance coil in series. Use the 
third pair of wires in same manner for the magnet. 

This hook-up is shown in Fig. 39. After the D. P. 
S. T. switch is closed, by operating the S. P. S. T. 
switches, any one device may be put in use or any com¬ 
bination made that you desire. 

Close all the switches. A current flows and you 
would like to know how it splits. Notice that the 2 
volts pressure is applied to each circuit just as if the 



Fig. 39. Parallel Circuits. 


others were not there. Convince yourself of this by 
opening first one and then another of the S.P. switches. 

These circuits are all independent and each has a cur¬ 
rent in it equal to its resistance divided into the voltage 
of the cell. The current flowing from the cell will be 
equal to the sum of the currents in the branch circuits. 

If you have an ammeter you may test this by insert¬ 
ing the ammeter in the places marked a and then in the 
wire from the cell. 

Joules Law.—The toaster and all such heaters 
are devices containing wires whose resistance is so great 
that the electrons in pushing through create a friction 
that causes heat. 

Every heating appliance that you purchase should 














MEASURING ELECTRICITY 


157 


have a label on it, telling how many watts of power it 
uses up. Multiply by the number of seconds you have 
used the appliance, then divide by four. This gives 
you the calories of heat produced. The calorie is the 
unit of heat used by scientists. Engineers are more 
apt to use the B. T. U. for their heat unit. This B. T. 
U. is the amount of heat required to raise the tempera¬ 
ture of one pound of water one degree Fahrenheit. 

I Square R. —When an engineer uses this phrase 
he is talking about I 2 R. If you multiply the square 
of the current in amperes by the resistance of the cir¬ 
cuit in ohms you find out how many watts disappear 
in heat. 

Problem. —A toaster on a 110 volt circuit takes a 
current of 5 amperes. Its resistance is 22 ohms. How 
many watts does it use ? How many watts are turned 
into heat? 

1. —Watts = amperes X volts 

= 5 X HO 
— 550 watts 

2. —Watts = (amperes) 2 X °hm 

= (5X5) X 22 
= 25 X 22 
= 550 watts 

It uses up 550 watts and turns them into heat. 

Why Big Wires. —When you think of the 
i square r 

loss you realize that the larger the wires carrying cur¬ 
rent to a place the less power is turned into heat and 
thus lost. 

But, and this is a great big but, since to find the 
power lost in heat while the power is being brought to 
a place we square the amperes, before multiplying by 
the ohms, it is the current that counts the most. The 
size of the current is the vital factor in the I 2 R loss, 
which is power lost in heat. 


158 THE BOYS’ BOOK OF ELECTRICITY 


Why High Voltage.—There are many combina¬ 
tions of amperes and volts which will bring one kilo¬ 
watt of power to you. Let us figure out a few. One 
kilowatt equals 1000 watts. Hence 1000 amperes at 
1 volt pressure, 100 amperes at 10 volts, 10 amperes 
at 100 volts, 1 ampere at 1000 volts, all will deliver 
1000 watts of power. Well, what is the difference? 



DELIVERING POWER IN DIFFERENT WAYS 


WATTS 


<R. 

, .WATTS $ 

POWER LOST IN HE A T DURING DELIVERY! 


Fig. 40 . Losses in Transmission. 


As far as the consumer is concerned, there is no dif¬ 
ference except in the price charged. But a watt is 
a watt, you will say. Why the difference in price ? 

Seeing things expressed in diagrams or charts helps 
the mind to grasp them. Look at Fig. 40. The iE and 
el express the idea that power may be delivered in 
different ways. You also see that a small current may 
be delivered through a high resistance with a small 
expense for the watts lost in heat. A large current, 
although delivered through a small resistance, causes 
a large and expensive loss in watts. 









MEASURING ELECTRICITY 


159 


The worst is however yet to come. A low re¬ 
sistance means large wires and these copper wires are 
expensive. 

So the proper way to deliver watts will be by means 
of a high voltage and a low current through a moderate 
resistance. In this way the loss is kept down and the 
expense for copper wire made reasonable. 

Drop. —Do not think that all our troubles in the 
transmission of electricity are solved. We still have an 
unavoidable drop to contend with. 

To push electrons through resistance requires pres¬ 
sure, and a definite amount of that pressure is used up 
in the process. You cannot avoid this loss. 

We call this loss drop. It is an old term that came 
into use because engineers pictured the current as drop¬ 
ping its pressure as it passed through resistance. So 
they said that there was a drop in the voltage. 

The drop is calculated by the formula: 

Drop = amperes X °hms, or expressed in letters: 

V = ir 

Modern engineers frequently refer to drop as the 
“eye-are loss.” This, as you see, refers to the method 
of calculating it. 

When one end of a long transmission line is kept at 
30,000 volts, at the other end the pressure will be 
about 29,000 volts. The drop or ir loss being about 
3 per cent of the e. m. f. 

The electric company may keep the end of the cir¬ 
cuit at their power station at 125 volts, but the un¬ 
avoidable drop on the line will result in a pressure of 
about 120 volts at your home. 

Warning .—Do not mix up the i 2 r loss, which is a 
loss of power which wastefully heats the wires, and the 
ir loss which is a loss in the pressure. 

Behavior of A. C. —Alternating current just 
naturally dislikes coils of wire. When d. c. goes 


i6o THE BOYS’ BOOK OF ELECTRICITY 


through a coil it makes a magnet and after that there 
is no more fuss. It is true that the current takes per¬ 
haps a second to get the magnetism built up, but after 
that second or fraction of a second the current which 
flows can be calculated by Ohm’s Law. 

When the electrons of a. c. start through a wire they 
build up the magnetism, but when they stop, just before 
they reverse their direction, the magnetism dies away. 
Then the electrons move back and build up the opposite 
kind of magnetism. This building up, dying down, 
rebuilding of magnetism in cycles uses up a lot of 
energy. This results in a smaller current of a. c. in a 
circuit containing coils, than the d. c. current would be. 

It appears, then, that with an a. c. voltage sending 
current through coils you can not calculate the amperes 
by Ohm’s Law. A circuit offers more resistance to 
a. c. than to d. c. This extra resistance to a. c. we call 
reactance, and the sum of the resistance and the re¬ 
actance we call impedance. The actual calculation of 
these new factors we will leave for more technical books. 

The Three Wire Circuit. —I have left this until 
the end of the chapter because I wanted you to have 
the contents of this chapter in your heads while build¬ 
ing this model, which will let you see the arrangement 
of the wires in this method of delivering power. 

Experiment 26.—A Model Electric Lighting 
Circuit. —You will need two dry cells, a porcelain 
three-wire, main-line plug cut out, three plug fuses for 
this, four 1.5 volt flash light lamps, and four sockets 
for them. The few feet of wire required you probably 
have on hand. If you can only purchase 3 volt lamps, 
buy four dry cells and use two wherever I say one. 

A Two-Wire Circuit .—Arrange the cell, the fuses in 
their plug cut-out as shown in Fig. 41. Use only two 
of the three fuses in the cut-out. Attach the'three 
branches to the main lines by soldering. In these 


MEASURING ELECTRICITY 


161 

branches connect the lamp sockets or receptacles* Notice 
that in one branch there are two lamp sockets in series. 

When you feel that you have gotten everything cor¬ 
rect and shipshape mount this model on a board. 

The reason for using such a big clumsy cut-out is to 
remind you that this or its equivalent is in your home 
at the place where the service wires first pass through 
its walls. Also, being a standard device, it can be pur¬ 
chased everywhere. Further, it is about the cheapest 



fuse holder that can be bought. We are planning to 
use the fuses as switches. 

Take out the two fuses and you will see that the 
lines beyond them are dead. For this reason when 
repairs are to be made to the house wiring one should 
remove the fuses from the cut-out that controls the 
circuit. 

Replace one fuse and notice that one side of the cir¬ 
cuit is now alive. If a wire fell on your model so as to 
bridge across the gap, caused by the absence of the 
second fuse, then a current could flow. A circuit is 
never dead unless both fuses are removed. 

Place both fuses in the cut-out and the lamps in the 
branches which have single sockets. Notice that they 
operate independently. These lamps are in parallel on 
the main circuit. 

Now place two lamps in the branch that has the two 
sockets in series. Note that the lamps burn very dimly, 
for each lamp is under half its normal pressure. Notice 
that when one lamp is turned out, the other is also 










162 THE BOYS' BOOK OF ELECTRICITY! 


extinguished. These lamps are in series and so act a$ 
a unit. 

When you have learned all you can by turning lamps 
on and off, you are ready for “stunts.” Be sure that 
you are using a dry cell or cells as your source of 
power before you do this part of the experiment. 

Take a piece of bare (not insulated) wire about a 
foot long and lay it across the wires in every place and 
way that you can think of. Keep it on the wires just 
long enough to see clearly what happens, then take it 



off and think out the explanation. Leaving these short 
circuits and crosses on the lines too long will wear 
out the cell. 

Be sure to try the effect of using the wire as a shunt 
around one of the two lamps that are in series. Notice 
how the other lamp increases in brilliancy. 

A Three-Wire Circuit. —Experiment 27.—Fol¬ 
lowing the hook-up given in Fig. 42 you will have no 
difficulty in setting up this model of a three-wire system. 
Two things are to be noted. At first do not connect the 
branch shown in dotted lines. Do not attach the feeder 
to the neutral wire exactly as shown in the diagram. 
For clearness I have shown this feeder attached mid¬ 
way between the cells. This makes it clear that the 














MEASURING ELECTRICITY 163 

neutral or middle wire is positive to the upper line but 
negative to the lower line. For that reason it is marked 
both and —. 

From the diagram you can see that the neutral feeder 
is under the influence of a zinc and a copper electrode 
at the same time. Thus it is proper to call it neutral. 

In the actual set-up the neutral feeder could be at¬ 
tached to the nearby zinc electrode or to the nearby 
copper electrode. The electrical result would be the 
same as that obtained by connecting exactly as shown 
in the hook-up. 

Insert the three lamps. Consider the flow of the 
electrons, which is opposite to the direction of the flow 
of current. 

The electrons for the two lamps flow down the nega¬ 
tive wire and passing through the lamps, find two paths 
open to them. The path through one lamp will only 
carry half of the electrons, so they split. Half go back 
by the lamp and half by the neutral wire. 

The lamps and appliances of any house or factory 
are so distributed over the two parts of a three-wire 
system, that of those devices apt to be used at the same 
time, half are on each part of the system. The elec¬ 
trician says “Half on each side/’ 

Suppose the division to be skillfully made. The neu¬ 
tral wire carries a flow of electrons just equal to the 
amount of lack of balance of the load. 

Now connect in the branch shown in dotted lines 
and insert a lamp in it. Now all the electrons coming 
down the negative wire may pass through and go back 
on the positive wire. 

To prove that they are doing this, you may take out 
the fuse in the neutral wire. This cuts off the neutral 
feeder, yet the system is not affected. The neutral wire 
is there to carry electrons for the unbalanced load. 
Hence the neutral wire can be one half the size of the 
other two. 


164 THE BOYS’ BOOK OF ELECTRICITY 


The saving in money that would be spent on copper 
is very large. In the larger cities where hundreds of 
thousands of dollars’ worth of copper is in the service 
mains, this saving is very important. 

You must now experiment a little, turning off lamps 
here and there, making all the short circuits you can, 



making crosses between the wires at different places, 
until you know a three-wire circuit. 

Be sure to try the effect of an unbalanced load when 
the neutral fuse is out. 

In many places there is no fuse in the neutral wire 
and it is grounded. This prevents 220 volts being acci¬ 
dentally put on the 110 volt devices on one side of a 
three-wire system. 

In Your House.—I f a three-wire service enters 
your home you will not find three wires running to the 
lamps and appliances throughout the house. 

The neutral will be split and it, with one of the out- 




































MEASURING ELECTRICITY 165 

side wires, meaning the positive or the negative wire, 
will be carried as a pair through the house. 

Thus two two-wire circuits in the house, whose prob¬ 
able loads seem to be equal, will be attached to a three- 
wire supply as shown in Fig. 43. 

110 Volt Control Panel. —Experiment 28.—Your 
study of the model circuits that you have built out of 
the house wiring system should have taught you to 
avoid certain things. 

You ought now to be able to build and operate a 
device for connecting 110 volt lines to your experi¬ 
ments. Remember that your friends will want to see 
your work in operation. They will want to see just 
what you do. “Please let me try it” will be a frequent 
request. So you must have things neat, shipshape and 
fool-proof. 

First we want a hook-up as shown in Fig. 44. Then 
we want a full size lay-out, which you will make on 
heavy paper. Finally we will mount the apparatus on 
a base board, using the lay-out as a guide. 

When you start to build something from a hook-up 
diagram, you should proceed in a regular and orderly 
manner. 

Always make a copy of the hook-up on a sheet of 
paper large enough to make notes on. Check your copy 
with the diagram in the book, wire for wire, seeing 
that you know clearly what apparatus is meant by the 
different symbols. 

The hook-up in Fig. 44 shows an attachment plug 
at A connected to a porcelain two-wire main-line plug 
cut-out. One of the wires from this leads to a porcelain 
moulding receptacle and from this to another one of 
them. These are shown at B. With these come caps, 
shown at C. These caps are to be wired. To the wires 
at R and M may be attached resistances or an ammeter. 

Should you not wish to use these wires for inserting- 


166 THE BOYS' BOOK OF EEECTRICITY 




THE SET-UP 

Fig. 44. 110 Volt Control Panel. 
































MEASURING ELECTRICITY 


167 


resistances or meters into the circuit, you may twist 
these wires together to complete the circuit. This will 
not cause a short circuit because there are lamps in the 
circuit. 

The wire from the second receptacle is attached to 
one side of three porcelain moulding lamp receptacles. 
These have lamp sockets in them at E. To the other 
side of these a wire is attached which goes to a recep¬ 
tacle F, exactly like the one at B. From the other side 
of F a wire leads back to the cut-out. The experiment 
is connected to the cap G. 

The Lay-Out .—This device could be laid out on a 
long narrow board, but it will be much more con¬ 
venient to handle and stow away when not in use if 
its dimensions are changed. 

To make the lay-out which I have indicated, start 
with a sheet of heavy paper or thin cardboard. Assem¬ 
ble the apparatus on this in the arrangement of the lay¬ 
out. Draw the wires as pencil lines and then carefully 
compare the lay-out with the hook-up, to see if they 
are the same electrically. 

When all is arranged, run your pencil around the 
different pieces to mark their positions. Remove the 
apparatus. Trim the paper to a convenient size and 
hunt up a board for the set-up. 

The Set-Up .—Upon the board that you have selected 
as a base lay the paper lay-out, and with a nail punch 
holes through in enough places to accurately mark the 
places for the different pieces. 

Now screw down the seven pieces of porcelain, wire 
them up with rubber-insulated wire and insert the two 
fuses. The three caps and the attachment plugs are 
to be wired, and then we are finished. In wiring the 
caps and attachment plugs take great care that the bare 
ends of the wires near the attaching screws are not 
near each other. Only remove the insulation at the 
spot that is going under the screw head. 


168 THE BOYS’ BOOK OF ELECTRICITY 

Its Operation .—Insert 2 ampere fuses in the cut-out. 
In the lamp sockets at E place 110 volt incandescent 
lamps. The greater the number of watts mentioned 
on the label of the lamp, the greater will be the current 
that the lamp will allow to pass. Divide the watts on 
the lamp label by 100 and you will have the amperes 
that the lamp will pass. To be exact you should divide 
by the actual voltage in your home. 

The lamp receptacles D are in parallel, hence the 
current passed by each lamp adds its value to that passed 
by the others. Current will flow if one lamp is inserted. 
After that more lamps or lamps of higher wattage will 
increase the current. 

The wires from any of the caps C or F may be con¬ 
nected together without causing a short circuit. Be 
very careful of the wires up to the cut-out, for your 
fuses do not protect these wires. 

This device will operate on a. c. or d. c. and with any 
lamps from the 104 volt lamps up to 220 volt ones. 
The latter are seldom on sale. Should you use this at 
a summer home with a private lighting plant, the volt¬ 
age will probably be about 30, and so you should use 
the lamps that are sold for such systems. A 110 volt 
lamp on a 30 volt circuit will only allow about h of 
the current to pass that it would on its proper circuit. 

I 

Polarity Indicator. —If you have a d. c. supply 
you may charge a storage battery by using the 110 volt 
control panel. Do not connect the battery to G yet. 
Take the wires from G and touch to a polarity indi¬ 
cator and then when you have found which is the posi¬ 
tive wire connect it to the positive pole of the battery. 

Making a Polarity Indicator. —Experiment 29. 
—If you can find a tube with a ]/ A inch or larger bore 
(hole inside) you will avoid much trouble. If you can 
not find one you must make one from a small test tube. 


MEASURING ELECTRICITY 


169 


One three inches long is most convenient, but the length 
is not of real importance. Soften the bottom of the 
tube by heating it red hot. A wire held by pliers so 
that but *4 i nc h projects can be thrust through the 
softened glass. Keep the glass in or near a small flame 
to cool it slowly. The wire will be welded into the 
glass. 

Thrust a wire through a cork that will fit the other 



Fig. 45 . A Polarity Indicator. 


end of the tube. If you found a tube with openings at 
each end you should fit corks in these. 

Make a solution of salt so strong that some salt re¬ 
mains in the bottom of the glass undissolved. Dis¬ 
solve one gram or 6.5 grains of phenolphthalein powder 
in a teaspoonful of medicated alcohol. Add half of 
this solution to enough salt solution to nearly fill your 
tube. The solution should be colorless. If it is pink, 
then the salt was not absolutely pure or your glassware 
not clean. In this case mix ten drops of vinegar in a 
third of a glass of water and add a drop at a time to 
the salt solution until it is colorless. 

Fill the tube nearly full, insert the cork and you are 
ready for a test. 

Touch the wires from a cell, or some d. c. supply, 
and the end which turns pink is the negative wire. 
Shake up the solution and the color will disappear. 

Don'ts for 110 Volt Circuits. —1. Do not turn 
on the current until you are sure that the experiment 
is set up exactly like the hook-up; and that all loose 
wires and tools have been put away. 

2. Do not use “any old fuse.” Use those with the 
smallest current capacity possible. Better blow a fuse 
than blow your apparatus. 




170 THE BOYS’ BOOK OF ELECTRICITY 


3. Do not open and close circuits at the key or chain 
of the socket, nor at the attachment plug. Use a switch 
in the circuit or the cap G of your panel. 

4. Do not leave your experiment connected to the 
house supply when you leave the lab, although it is 
just for a moment. At least pull out the cap G, and 
better yet, also take out the attachment plug A. 

5. Do not work in a hurry. Many a dinner has 
been eaten by candle light because just as “Dinner is 
served” floated up stairs, the son hurriedly connected 
a rush job to the house system. Instead of working, 
it blew. 


CHAPTER VIII 


HOW ELECTRICITY COMES TO US 

Conductors 

Leaders 

The Wires in a House 
The Underwriters’ RueES 
Materials for Conductors 
Comparison of Conductivity 
Experiment 30 

Measurement of Resistance 
Resistance by Substitution 
Experiment 31 

Resistance of a Galvanometer 
Experiment 32 
Relative Resistances 
Wire Tables 
Table A 
Table B 

Use of a Wire Table 
Effect of Temperature on Resistance 
Experiment 33 
The Underwriters 
Uses of Resistance 
Two Ways of Explaining 
Our Old Friend I 2 R 
Laws of Resistance 
How a Wire Conducts Electricity; 

Insulators 


171 


1 




\ 









CHAPTER VIII 


HOW ELECTRICITY COMES TO US 

Conductors. —The wire that brings the electrons 
to us is called an electrical conductor, but this is not a 
perfect name for the things that persuade the electricity 
to go in a particular path. The word conductor reminds 
me too much of a conduit, which is a hollow affair. 
Now, electricity does go through a wire, but also on 
and around the wire. 

Leaders. —When a boy, I watched the plumber 
put new pipes down the outside of the house, to carry 
the rain water down from the roof. He called them 
“conductors,” but I called them “leaders.” He used 
his name because they conducted the water, and I used 
my word because they led the water. Well, we were 
both right. 

I have often thought of a situation in which my 
name of “leader” would be the better name. Suppose 
a new kind of rain began to fall. The burning ques¬ 
tion, if I may use such a word in reference to very wet 
water, would be, “How will this new kind of rain act ?” 
On rushing out to see, every one would be amazed at 
this new rain. It would come sliding down the roof, 
turn suddenly at the edge and flow along the outside 
of the gutters to the leaders and then down the outside 
of the leaders to the ground. Yet it would cling close 
to them as if by magic. Then truly the leaders would 
be leaders and not conductors. 

173 


174 THE BOYS’ BOOK OF ELECTRICITY 


For high frequency alternating currents the wires 
act more like leaders, while for low frequency a. c. and 
for d. c. they act like conductors. Since the current 
always uses some of the wire to travel upon, we use 
the same material to persuade all kinds of current to 
come to the place where we want the electrons, and this 
material is copper. 

We are always trying to persuade electrons to come 
to us from the place of high pressure, do some work, 
and go back home. Rather, since an electron has no 
real home, we want it to go back to where it obtained 
its force and get a new supply of push and pep. We 
must try to make the trip an easy one. To do this we 
use copper. 

The Wires in a House. —Investigation of the 
wires around a home show that two conductors usually 
are bound together by a covering to protect them from 
wear by friction or by bending. Inside the walls or on 
the cellar ceiling you may find this cable or cord of two 
conductors drawn into a system of iron pipes to pro¬ 
tect them from hammer blows, or nails driven during 
repairs to the building. 

Sometimes the cord is covered with a flexible inter¬ 
locking metal armor. This is called BX by the elec¬ 
trician. 

The two wires inside of the outer protection are each 
covered with rubber and cotton. Often the copper 
conductors are each composed of many fine wires 
twisted together. This makes the conductor flexible. 
The wires in the walls are solid copper. 

All movable appliances such as irons, toasters, grills, 
heaters, floor lamps, vacuum cleaners and such devices 
have an extra cotton covering on the flexible cord. This 
in turn may be covered with silk to improve its ap¬ 
pearance. 

But why all this fuss? Why the rubber and the 
cotton, why the careful protection? 


HOW ELECTRICITY COMES TO US 175 


The Underwriters’ Rules. —A group of men have 
made a set of rules to protect ignorant folks, so that they 
won’t lose electricity by leaks nor get too many elec¬ 
trons in one place at one time. Either of these things 
may create enough heat to start a fire. 

The fire insurance people, or the underwriters, as 
they are called, have by experience learned how wires 
should be protected. We must have the wire guarded 
from wear and tear, from mechanical injury due to 
accidental blows, and there must be a rubber covering 
to prevent the electrons from leaking off the wire. The 
underwriters maintain a laboratory where all new elec¬ 
trical devices are tested for their mechanical protection 
of the wires and for the character of the insulation on 
the wires. 

No device should be used in a building upon which 
fire insurance is carried unless it has been approved by 
this laboratory. No wiring nor additions to the wiring 
of such a building should be used until the proper 
officers have inspected this wiring and issued a cer¬ 
tificate. 

Should a fire occur and you have no certificate the 
insurance company may properly refuse to pay any 
insurance until it has lien proved that no wiring or 
electrical appliance was the cause of the fire. 

Experience has taught us that for portable apparatus 
solid wires are stiff and clumsy. They would soon break 
by the constant bending and kinking to which they are 
subjected. For that reason all portable appliances are 
connected by stranded wires. 

A few paragraphs ago I was mentioning insulation. 
We are not quite ready to discuss it. The voltage of 
my brain made the current of my thoughts run ahead 
too fast. I will throw a few ohms in my mental circuit 
and slow up, to turn back to the discussion of con¬ 
ductors. 


176 THE BOYS’ BOOK OF ELECTRICITY 


Materials for Conductors. —Silver and copper 
conduct electricity and lead it with about the same ease. 
Just as every crowd offers some opposition or re¬ 
sistance to folks walking through it, just as the air 
offers resistance to the passage of an airplane, so does 
every material offer resistance to the passage of elec¬ 
trons. 

Comparison of Conductivity. —We use the ohm 
as a unit of resistance to compare the conductivities of 
materials. The ohm has been defined in Chapter VII 
but there are several ways of forming a resistance of 
one ohm in a practically accurate way. 

Two pounds of bare (uninsulated) No. 16 copper 
wire, 250 feet of No. 16 copper wire, 62 feet of No. 
22 copper wire, 9 feet 7 inches of No. 30 copper wire. 
Any one of these pieces of wire has about one ohm 
of resistance, near enough for you to use these as units 
of measurement. 

Experiment 30.—Using No. 30 cotton-covered wire, 
wind on empty spools a series of resistances. If you 
will make one 1 ohm, two 2 ohms, one 6 ohms and one 
12 ohms, you will be able to obtain all the combinations 
from 1 to 23 ohms. Two feet four inches make one 
ohm when No. 30 copper wire is used. 

You will need a connection board so that any com¬ 
bination of these resistances can be quickly made. Select 
a piece of smooth wood about eight inches long and 
one or two inches wide. Drill or burn holes half way 
through the wood at equal distances apart, say about 
one inch. Fill these holes with mercury. 

The use of this connection board is apparent in Fig. 
46. Placing the ends of a coil in the holes places it in 
the circuit. The jumpers should be made of heavy 
wire or, as shown, of ordinary wire bent so that four 
wires carry the current. All ends should be sand¬ 
papered bright and clean before insertion in the mercury. 


HOW ELECTRICITY COMES TO US 177 


Set up a series circuit with a few cells, the connection 
board, and the galvanoscope with the shunt coil B at¬ 
tached to it, like Fig. 47. 

Vary the resistance of the circuit by inserting in suc¬ 
cession the coils you have just made. 

By the change in the galvanoscope reading you can 
tell which coils are high and which are low in resistance. 
Selecting any two coils, by placing first one and then 
the other in the circuit, you can tell which is the higher 



resistance. But since the coils are not the only re¬ 
sistance in the circuit the changes in the current as shown 
by the galvanoscope are not proportional to the re¬ 
sistances of the coils. 

Measurement of Resistance. —The method of 
substituting known resistances for the unknown until 
the current is brought to its previous value makes use 
of the principle called Ohm’s Law. 

If the voltage is the same and the current is the same 
then the two different resistances used are equal. 

Resistance by Substitution. —Experiment 31.— 
Select some coil whose resistance you do not know. 
Set up the experiment from the hook-up given in Fig. 
47. The switch, or push button, could be omitted and 
the current broken by using a jumper. If the deflec- 







178 THE BOYS’ BOOK OF ELECTRICITY 

tion of galvanoscope is too small when the unknown 
coil is in the circuit then use two cells. 

Remove the unknown coil from the circuit but leave 
everything else exactly as it is. Substitute for the un¬ 
known coil such a combination of your resistance coils 
as will make the galvanoscope give the same deflection. 
The resistances you have put in are equal to the un¬ 
known resistance that was in the circuit before. 



Fig. 47. Hook-up for Measuring Resistance. 


The reason is, that with equal voltages the same cur¬ 
rent is passed by equal resistances. 

Resistance of a Galvanometer. —Experiment 32. 
—You may have only one galvanometer and wish to 
know its resistance. Here is a method for finding the 
resistance of a galvanometer while using it to give the 
readings needed. 

The method is called The Half Deflection Method. 
Connect the galvanometer in series with a cell and the 
connection board. Add enough resistance to give a 
deflection of about half way up the scale. Our gal¬ 
vanometer reads from 0 to 8. Adjust the added re¬ 
sistance until the deflection is about 4. Call this re¬ 
sistance R. 

Do not disturb any of the circuit except to remove 
jumpers and insert more resistance into the circuit until 
the galvanometer reads half the previous deflection. 










HOW electricity comes to us 


179 


The total resistance now connected to the circuit by 
means of the connection board we will call r. 

The resistance of the galvanometer will be r—2R. 

For an example. With 5 ohms inserted at the con¬ 
nection board the reading of the galvanometer was 4. 
With 7 ohms added, or a total of 12 ohms, the deflec¬ 
tion was reduced to 2. The resistance of the galvano¬ 
meter was 12 — (2X5), which is 12 — 10 = 2 ohms. 

You might also find the combined resistance of the 
galvanometer with coil A in series and the combined 
resistance of the galvanometer with coil B in parallel. 

Relative Resistances. —The resistance of a piece 
of silver wire might be 98 ohms. Then the resistance 
of a copper wire of exactly the same size and shape 
would be 108 ohms. You see that it would not pay to 
spend a lot of money for this small increase in con¬ 
ductivity. 

If the wire we were talking about had been of 
aluminum its resistance would have been 172 ohms. 
This would seem to kill the idea that aluminum might 
be used in place of copper. But for the same con¬ 
ductivity the aluminum wire, although larger, has only 
half the weight. When wires for the transmission of 
power are carried across the country on steel masts, 
such as are shown in the Frontispiece, weight counts. 
Such wires are often made of aluminum. 

Wire Tables. —Engineers who are designing ap¬ 
paratus need a lot of information about wires. The 
diameter, the number of feet in one pound, the re¬ 
sistance of 100 feet, the number of feet in one ohm of 
resistance and the current that the wire will carry with¬ 
out too much heating, are all needed at one or another 
time in his work. 

For such information he uses a wire table. You will 
not require a complete table, so I am giving you the 
information that will be of greatest service. 


i8o THE BOYS’ BOOK OF ELECTRICITY 


Table A . — This table is for bare, that is, not insulated 
copper wires. For experimental use, the carrying ca¬ 
pacity of a wire is that current which will permit you 
to hold the wire in your hand. If you use a larger 
current, the heat may be stored up in poor conductors 
of heat, such as paper, which catches fire easily. 

Resistance coils that you are planning to run at high 
temperatures should be insulated with asbestos and 
porcelain, then mounted on metal and slate. 

Table B .—An alloy of nickel, copper and zinc, called 
German silver, makes a smaller coil for a given re¬ 
sistance. This alloy is named, in the stores, according 
to the percentage of nickel in it. Eighteen per cent wire 
has that per cent of nickel in it. Thirty per cent wire has 
higher resistance and higher cost. 

Use of a Wire Table. —Suppose I wish to wind a 
5 ohm coil and I have a spool of No. 30 copper wire. 
From the table I find that this wire has a length of 9.7 
feet for every ohm of resistance. Multiplying by 5 
gives 48.5 feet as the required length. 

Suppose two telephone receivers have a resistance of 
3000 ohms, which is 1500 ohms for each one. They 
are wound with No. 36 copper wire. How much wire 
on each one? A resistance of one ohm requires 2.4 
feet, hence each receiver contains 2.4 X 1500, or 3600 
feet. The two contain over a mile of wire. 

Effect of Temperature on Resistance. —Some 
wires made of patented alloys do not change their re¬ 
sistance with the temperature. Expensive but very 
accurate measuring devices use coils of such wires. 

Copper increases in resistance as it increases in tem¬ 
perature, but not enough for us to worry about unless 
we attempt to force large current through small wires. 

Effect of Temperature on Resistance. — Ex¬ 
periment 33.—On a piece of asbestos wind a coil of 10 
feet of No. 30 bare iron wire. Connect this in series 


Table A—The Properties of Copper Wire 


HOW ELECTRICITY COMES TO US 181 



* Note that this refers to a bare or uninsulated wire. 






































Table B—The Properties of German Silver Wire 


182 THE BOYS’ BOOK OF ELECTRICITY 
























HOW ELECTRICITY COMES TO US 183 


with the galvanoscope with its shunt coil B attached 
to it. Support the coil of iron wire above the bench 
by glass rods. 

Connect as many cells as are needed to give a deflec¬ 
tion of half the scale. Then with an alcohol lamp or 
Bunsen burner heat the wire hot. The indication of 
the meter will lessen, showing that a smaller current is 
flowing. 

The Underwriters have set certain limits for rub¬ 
ber covered wires on 110 volt circuits, when the wires 
are enclosed in the walls or in mouldings. The limit 
for a No. 18 wire is 3 amperes. This size is called 
fixture wire, for it is used in wiring chandeliers, floor 
and table lamps. The No. 14 wire, which is the small¬ 
est size used in the walls or in BX, may carry 12 
amperes. 

The fire insurance people are afraid of the heated 
wire causing a fire. They do not want a heated wire 
to cook its rubber insulation to a brittle material, which 
would crack and lose its insulating properties. 

Uses of Resistance. —Wires of nickel silver, Ger¬ 
man silver, bronze, chromel, Krupp alloy, bronze and 
steel are used either to choke off undesired volts and 
thus reduce the flow of electrons, or to offer such an 
opposition to the passage of the electrons that the wires 
will grow hot. 

You may have a lamp in a child’s bedroom or in a 
bathroom. This lamp you wish to use at a very low 
candle power and yet be able to turn on at full candle 
power instantly. 

The double filament lamp solves the problem. But 
this requires a special lamp. There is a device made 
like a lamp socket which is a variable resistance. Pull¬ 
ing the string dims the light. Why? Because there 
has been put into the circuit enough ohms to use up and 
destroy part of the 110 volts pressure. The remaining 


184 THE BOYS' BOOK OF ELECTRICITY 


pressure cannot force enough electrons through the 
lamp to light it to normal brilliancy. 

There is another way of explaining this. When you 
pull the string you add a resistance to the circuit which, 
with the resistance of the lamp, makes the total re¬ 
sistance too great for the normal current to flow. Less 
current, less heat, so the lamp gives less light. 

Two Ways of Explaining. —This is a good place 
to tell you that quite frequently two persons may give 
different explanations of the same thing. That is, they 
explain the same thing from a different standpoint. 
They thus get the facts at a different “slant." When 
these two explanations are carefully gone over you 
will find that they are both correct. Probably one ex¬ 
planation will get into your head and stick there better 
than the other. It is for this reason that I advise you 
to talk over problems with all your friends and teachers. 
If doing this merely confuses you, then your elementary 
and fundamental knowledge is lacking in quantity or 
quality. Improve both by reading, experimenting and 
thinking. 

You cannot get along without books, for you may 
have them with you at all times. But when the real 
live person who knows is around, leave the books and 
get him to talk. 

Our Old Friend I 2 R. —A power transmission 
engineer would not like me to call I 2 R a friend, be¬ 
cause when he transmits power from a waterfall to a 
city he does not care to heat the air between them. Yet 
he can’t help doing some heating. There is the re¬ 
sistance of his transmission line, and its effect is to 
produce heat when the electrons pass through it. 

You and I want toasters and electrical heaters, so we 
put a lot of resistance in a small place and count the 
heat produced as useful, not as a loss. 

We do not want to heat the walls of the home, so 


HOW ELECTRICITY COMES TO US 185 


we use large wires of low resistance to bring the cur¬ 
rent to the place where we will use it. 

Laws of Resistance. —1. The resistance of a con¬ 
ductor is the same for all values of current unless the 
current heats the conductor. 

2. For copper wire, the higher the temperature the 
greater the resistance. 

If resistance is 10 ohms at 70° Fahr., it will be 12 
ohms at 125° Fahr., and 13 ohms at 180° Fahr. 

3. For direct current and low frequency alternating 
current it is the area of the cross section of the wire 
which conducts. 

Hence resistance diminishes as the square of the 
diameter of the wire. Twice the diameter, one fourth 
the resistance of previous wire. 

4. For high frequency alternating current it is the 
surface also that leads the current. Hence stranded 
wires should be used. 

5. The resistance increases with the length of the 
wire. 

6. Every material has its own special resistance. 

By cross-section we mean the area of the end of the 
wire when it has been cut across perpendicular to its 
length. 

How a Wire Conducts Electricity. —A copper 
wire is composed of atoms, and these atoms of electrons 
and protons. Many of the electrons are held by the 
protons in the nuclei of the atoms, but the rest are 
quite a distance from the nuclei and free enough to 
wander from atom to atom. 

When an e. m. f. is applied to the wire these free 
electrons are urged in one direction and it is this move¬ 
ment of electrons in the conductors that we call current. 

Compare the wire to a sidewalk, as I have done in 
Fig. 48. The boys are the electrons. The sporting 
goods store, the candy shop, and other attractive show 
windows will represent the protons. The boys who 


186 THE BOYS' BOOK OF ELECTRICITY 


crowd up to those windows represent the electrons held 
firmly by the protons of each nucleus. 

The boys coming towards us are urged onward by 
an e. m. f. behind them (school is out), and also by a 
pulling force before them (there is food at home). 



Fig. 48. How a Wire Conducts Electricity. 


But there are always some electrons moving in the 
wrong direction, which cause friction and some heated 
words. 

Finally the onrush of electrons may be great enough 
to push some of the electrons off the wire into space, 
just as on our sidewalk the jostling and pushing has 
shoved two boys into the gutter. 

I am sure if some one in the rear called ‘Tire” 
that in the commotion that would result, it would be 
harder for any one boy (electron) to walk through 
the surging, swaying crowd. Thus the wire offers 
extra resistance to alternating current. 









HOW ELECTRICITY COMES TO US 187 


Now if a fight, a good “scrap” started in the center 
of the crowd and it swayed back and forth, in an 
excited way, at a high rate, I am sure still more boys 
(electrons) would be shoved off into the gutter. 

In the same way high frequency a. c. pushes many 
electrons of the wire into the adjacent space. 

Insulators. —There are materials like glass, por¬ 
celain, rubber, gutta percha, bakelite, paraffin, oils, 
resins, shellac, slate, mica, sulphur, silk, wool, cotton, 
paper, and dry air which, while composed of protons 
and electrons, will not conduct a current of electricity. 

Although subjected to the stress of high electron- 
motive forces, the electrons of these materials refuse 
to budge. As we have no flow of electrons, there is no 
transfer of electrical charges and no flow of current. 

These materials are called insulators . They are used 
to keep electrical charges and currents where we want 
them, and out of places where we do not want them. 




CHAPTER IX 

MAGNETISM 


Lodestone 

Origin of the Names 
To Make a Magnet 
Experiment 34 A 
Experiment 34 B 

Rule for the Polarity of a SoeEnoid 

Poles 

Forces Between PoeES 
Current and Flow of Electrons 
The Polarity of a Solenoid 
Watch Rule for Poles 
Rule for Winding Horse Shoe Magnets 
What is a Magnet 
Poles Come in Pairs 
Consequent Poles 
Magnetic Substances 
Cores for Electromagnets 
Permeability 
Retentivity 
Magnetizing Force 
Ampere-Turns 
Flux 

Lines 

Other Units 

Saturation 

Experiment 35 
Theory of Magnetism 
How Iron Becomes Magnetized 
Effect of Breaking a Magnet 
Experiment 36 
Magnetic Field 
Magnetic Induction 
Experiment 37 
Experiment 38 
Experiment 39 


189 


i9o THE BOYS’ BOOK OF ELECTRICITY 


No Insulator for Magnetism 
Experiment 40 
Side Tracking Magnetism 
Protecting Watches 
Experiment 41 
The Compass 
Declination 
Dip 

Experiment 42 
The Earth a Magnet 
Current Acts Magnetically 
Experiment 43 
Snow Rule 

Principle of the Galvanometer 
Further Experimentation 


CHAPTER IX 


MAGNETISM 

Lodestone. —As far back as 2800 years ago, the 
Greeks knew that this black stone, which is really an 
oxide of iron, attracted iron. Homer and Aristotle 
mention it. A Roman poet who lived before Christ 
was born tells how iron rings may be made to hang in 
a chain from a piece of lodestone. 

Origin of the Names. —This black iron ore oc¬ 
curred in large quantities in the district of Magnesia. 
Thus the name of Magnesian stone was applied to it. 
Later in England the name of magnet was coined from 
the name of the country where it came from. 

About the tenth century, it was discovered that a 
piece of this mineral when freely suspended, turned 
until it pointed in a north and south direction. 

This peculiarity gave it the name of leadstone or 
lodestone. 

Lodestone was used to magnetize pieces of iron and 
steel by stroking them. These artificial magnets were 
used by the Chinese as a compass, for sailing, about 
the year 1300. 

To Make a Magnet. —Experiment 34A.—Lay a 
piece of hard steel, such as a small drill or part of a 
hack saw blade on the bench before you. Hold a bar 
of magnetized steel in a vertical position and stroke the 
drill from end to end as shown in Fig. 49. 

If you use the N end of the magnet for stroking, the 
191 


192 THE BOYS’ BOOK OF ELECTRICITY 


part of the steel last touched at each stroke will be a, 
south pole. 

As magnets made by this process are not very strong, 
the practical use of magnets did not develop until the 
electro-magnet was discovered in 1825. 


Experiment 34B.—Twist a copper wire around a test 
tube or pencil. The shape of your coil is a helix. 
Connect the ends of this helix to a battery and current 



will flow, making it a weak magnet. This coil carrying 
a current we call a solenoid. See Fig. 50. 

Place a piece of steel in this helix and pass a large 
current through it, thus making it a solenoid. Although 
the current did not pass through the steel it will become 
magnetized. 

Practical Details .—Connect the nearer end to the 
carbon or + pole and the farther end to the zinc or — 
pole of the battery. One cell is shown, but five cells 
in series are needed to produce a strong magnet. 

While the current is passing, hit the steel several 
sharp blows with a piece of wood. 

Should your magnet be too weak although five cells 










MAGNETISM 


193 


are used, then the steel you have is very hard and 
difficult to magnetize. 

You will then connect the 110 volt control panel to a 
d. c. circuit, fill the lamp sockets with 50 or 80 watt 
lamps and then attach the helix. 

Rule for Polarity of a Solenoid. —If the set-up 
of your experiment followed exactly the hook-up given 


ARROWS SHOW DIRECTION OF CURRENT 
ELECTRONS MOVE IN OPPOSITE DIRECTION 



Fig. SO. Magnetizing Steel with Current. 

in Fig. 50, then the nearer end of the solenoid will be 
a south pole and the magnets made in this solenoid will 
have the same polarity as the solenoid. 

Poles. —The parts of a solenoid or magnet which 
attract or repel each other are the poles. The north 
pole is the part which points northward when the mag¬ 
net is freely suspended. 

The poles of a magnet are very near the ends of the 
material, but not, as you would suppose, exactly at 
the ends. 

Poles only occur where the material changes from a 
magnetic substance to a non-magnetic one. This is 




194 


THE BOYS’ BOOK OF ELECTRICITY 


why there are no poles along the magnetized bar, but 
only near the ends. 

If a helix is wound on a solid ring of iron and a 
current passed through the wire, no poles will be found. 
With a hack saw cut out a portion of this iron ring and 
remove it. Poles will develop on each side of the gap. 
Fig. 51 shows such a ring magnet. 

Forces Between Poles. —Like named poles repel, 
unlike named poles attract. It is evident then that the 
pole of a magnetized bar which swings around to the 



Fig. 51 . A Ring Magnet Showing no Poles. 

north is really of south polarity. But this end that 
swings northward has been called the north pole for 
so long that we keep the name although we recognize 
the error. 

The French, more accurate than we, called this end 
of the magnet the north-seeking pole. 

Current and Flow of Electrons.—Here also our 
names and the facts clash. For years we thought that 
the electricity, or whatever it was that we called elec¬ 
tricity, flowed through our apparatus from the carbon 
to the zinc pole. Many convenient rules have been 
devised and memorized by millions of men using this 
mental picture of current. Thousands of books con- 




MAGNETISM 


195 


tain valuable material and discuss electrical things, talk¬ 
ing about current as flowing thus. 

If we now, knowing that what moves in the circuit 
is a number of electrons and that they move from the 
zinc through our apparatus to the copper pole, change 
the definition of current, we will create endless con¬ 
fusion. 

All the old rules may stand; all our memorized 
knowledge be perfectly valid and valuable, if we say 



Fig. 52. Watch Rule for Polarity of Magnet. 

current when we mean current and flow of electrons 
when we mean the actual movement of the electrons. 

For example: Turn to Fig. 50. I glance at this 
illustration and say: “The current is flowing from the 
carbon through the solenoid to the zinc pole. The 
arrows show the direction of the current. But of course 
we all understand that this current is caused by a flow 
of electrons which move through the solenoid from the 
zinc to the carbon pole.” 

This should not be confusing. Remember that at 
the seashore the direction of the undertow is opposite 
to that of the incoming breakers. 




196 THE BOYS’ BOOK OF ELECTRICITY 


One must be careful to say current when current is 
meant and to say flow of electrons when that is meant. 

The Polarity of a Solenoid. —From Fig. 50 one 
might deduce the rule that when the current goes 
through a helix in a corkscrew fashion the nearer end 
is a south pole. 

Watch Rule for Poles. —When the current flows 



around a coil or helix in the direction of the hands of 
a watch, the nearer end is a south pole. This is shown 
in Fig. 52. This will enable you to wind bar magnets 
so as to have the desired pole at a definite end. 

Rule for Winding Horseshoe Magnets.—Hold 
the iron core with the parts which will be the poles 
facing you. Write on these the letters S and N, as 
shown in Fig. 53. Using the arrows on the letters as 
a guide, wind the two limbs or legs of the magnet. 
You must have the direction of the windings on the 
two legs reversed else both would have the same polarity. 

When the magnet is wound it will have the appear¬ 
ance of Fig. 54. The arrow in both Figs. 53 and 54 
show the direction of the current. The electrons are 
moving in the opposite direction. 




MAGNETISM 


197 


What Is a Magnet? —It seems about time to tell 
exactly what we mean by a magnet. Any piece of 
material which attracts magnetizable bodies and which 
when freely suspended turns in a north and south line 
is a magnet. 

A magnet has poles and can produce polarity in 
magnetic substances. By polarity we mean the nature 
of the magnetism at particular places. 



SOUTH WORTH 

ROLE POLE 


Fig. 54. A Horseshoe Electromagnet. 

Poles Come in Pairs. —No magnet, no matter 
how it was made, has less than two opposite poles. 
Some times in a long thin steel magnet there will be 
an extra pair of poles between the ones at the ends. 
This is due to a very hard spot in the steel or a very 
unequal magnetizing force exerted at different places 
along the bar. These are called consequent poles. 

Since the north and south poles of any magnet are 
but two different aspects of the same magnetic force, 
you will always find these two poles of equal strength. 




i 9 8 THE BOYS' BOOK OF ELECTRICITY 


Magnetic Substances.- —Iron, steel, nickel and 
cobalt may be magnetized. An alloy of manganese 
26.5 per cent, aluminum 14.5 per cent, and copper 59 
per cent has magnetic properties as good as cast iron. 
Besides a few other unimportant alloys, all other mate¬ 
rials are equally non-magnetic. 

Should you fill the solenoid of Fig. 50 with wood, 
paper, hard rubber, or paraffin the magnetic force will 
not be increased. All these materials seem to be equal 
in their dislike for conducting magnetism. 

Cores for Electromagnets. —Should cores of 
-various materials be made for a solenoid, and the 
strength of the magnet tested, as these are used in turn, 
the results will be as follows: 

Consider the magnetic force due to the solenoid as 
the standard. Then when a cast iron core is used in it 
the magnetic force will be 430 times as great. A core 
of a good grade of Bessemer steel gives a magnet 
whose force is 1150 times that of the solenoid. A 
wrought iron core is 1300 times better, and when the 
"very best grade of soft iron is used the magnetic force 
will be 1430 times as great as that given by the solenoid 
alone. 

Permeability. —The force that the combination of 
the current and the coil exerts cannot permeate the air 
as well as iron. In order to tell a person, quickly and 
accurately, what results may be expected from cores 
of different materials we use a number. 

We say the permeability is 99. Meaning that the 
•ease with which magnetism passes through the material 
spoken of is 99 times that of air. 

Many of our electrical devices such as bells, induc¬ 
tion coils, transformers and all alternating current ap¬ 
paratus using magnetism have iron cores subjected to 
intermittent magnetism or reversals of the polarity of 
the magnetism, or both effects. All these must have 
magnet cores of the very softest iron. 


MAGNETISM 


199 


This is not only on account of the high permeability 
pf this material but also because it will lose its mag¬ 
netism as soon as the magnetizing force is removed. 

Should the cores of the magnets in bells, sounders, 
[relays, and transformers retain their magnetic proper¬ 
ties after the current is cut off, several annoying things 
would happen. Their action would be sluggish, instead 
of quick and snappy, and the magnet cores would 
ibecome heated. 

Retentivity. —The ability to retain some magnet- 
jism after the magnetizing force has been removed is 
called retentivity. 

Usually this is a very annoying property, but there 
are places where it is valuable. 

The residual magnetism which is left in the magnets 
of a dynamo or generator when it is standing idle 
[enables the machine to start generating again when it 
is put into service. If its cores had no retentivity, 
they would require magnetization every time the gen¬ 
erator was started. Were it not for the retentivity of 
hard steel and the large quantity of its residual mag¬ 
netism, we could not have permanent magnets. 

Magnetizing Force. —The ability of a piece of 
lodestone or an artificial magnet to impart its proper¬ 
ties to a magnetic material I can not explain. There 
has been so much to investigate during the past ten 
years that the big scientists have not dug very deeply 
into this. Perhaps they will leave this for you boys 
to solve when you are a bit older. 

We do, however, know just what to do to make a 
: magnet, and we know what we will get when we use 
a certain sized magnetizing force. 

Ampere-Turns. —One turn of wire carrying a cur¬ 
rent of one ampere or two turns carrying half an 
ampere, etc., is what we mean by an ampere-turn. We 
know that two ampere-turns produce twice the mag¬ 
netism that one will. 



200 THE BOYS' BOOK OF ELECTRICITY 


So when you wish to compare two electromagnets, 
count the turns on one, multiply by the current and 
you have the magnetizing force. Do the same for the 
other. If the permeabilities of the cores are the same 
the magnetisms produced by each will be in proportion 
to the ampere-turns on each. 

Flux. —Magnetism is thought of as flowing like 
current, and so we speak of the magnetic flux or flow. 

Lines.—W e must have some unit for flux and so 
the unit of flux is called a line. This name was passed 
on to us by those who knew less than we do about 
magnetism. It is a poor name, but since we all know 
it we continue to use it. 

Other Units. —We have attempted to make people 
use certain words such as gauss, weber, maxwell and 
density or lines per square centimeter, in talking about 
magnetism, but at present only engineers and scientists 
use these names. 

Saturation. —When a magnet has about 800 
ampere-turns on each inch of its length we find that 
doubling the magnetizing force does not double the 
magnetic flux. In fact, for all practical purposes you 
have wasted the material used and the expense for 
current, for there is no increase in the flux. None? 
Well, the increase is so small that practically speaking, 
there is none. 

We call such a magnet saturated. As the material 
of the core approaches saturation it takes a greater and 
greater number of ampere-turns to produce equal in¬ 
creases in the magnetic flux. 

It is easy to find out that this does occur, and per¬ 
haps we can understand this action better if we con¬ 
sider the following experiment: 

Saturation. —Experiment 35.—Procure a short, 
thick rubber band and a bunch of butchers’ wooden 
skewers. Place a dozen skewers inside the band. Prac- 


MAGNETISM 


201 


tically no effort is required. Place another dozen in the 
band. A gentle pressure may be needed as you begin 
to feel the reluctance of the band to expand. 

The next dozen must be pushed in. The following 
dozen may need strong pressure, in fact you may be 
compelled to push them in one at a time. Towards the 
end you will find yourself driving the skewers in with 
a piece of wood or a small hammer. 

Evidently the ease with which the skewers can be 
placed inside of the rubber band depends on the number 
that are already there. 

Magnetic materials act in the same way when you. 
magnetize them. The more flux in them the greater 
is the magnetizing force needed to increase the flux. 

Theory of Magnetism. —In 1876 Rowland proved 
that a charge of electricity produced the same mag¬ 
netic effects as a current. This at once suggested 
that the magnetic qualities of lodestone were due to 
the revolving electrical charges in the molecule of the 
material. 

Until more was known about the constitution of the 
matter, this idea was but a theory which could not 
stand against the criticisms of scientists who were 
searching for the truth. 

Today we feel quite sure that electrons revolving in 
the molecules of a substance produce the effect that we 
pall magnetism. 

This theory is reasonable. If a coil or a single turn 
of wire bearing a stream of electrons will produce mag¬ 
netic effects, it is quite likely that the magnetism of a 
lodestone is due to streams of electrons, looping the 
loop, inside of the molecules. 

If we accept this theory we can picture to ourselves 
how a piece of iron may become magnetic. 

How Iron Becomes Magnetized. —In the mole¬ 
cules of the iron are some electrons revolving in orbits,. 


202 THE BOYS’ BOOK OF ELECTRICITY 


or we might say, looping the loop. This makes these 
molecules magnetized and gives them polarity. 

If the molecules are all jumbled up, as they probably 
are in a piece of iron, or in fact in any material, then 
we should expect their polarities to cancel and the mate- 


A 



3EFORE MA GNE T/ZA T/ON 


B 



AFTER MAGNTT/ZATiON 


Fig. 55 . How Iron Becomes Magnetized. 

rial to show no magnetism. Fig. 55 A shows this con¬ 
dition. 

When the magnetizing force of the ampere turns of 
a solenoid act on a bar of iron, the electrons are twisted 
around until they all revolve in the same direction. All ? 
Well, practically all. Then the polarities are arranged 
as in Fig. 55 B and the iron becomes a magnet. 

The stronger the magnetic force and the greater the 
permeability of the iron the more molecules are twisted 
around. 

The inherent possibilities of becoming a magnet are 
all there in the molecules of the iron, but it is the ampere- 
turns of the solenoid that lines up these conflicting 
forces and makes the magnet. 




MAGNETISM 


203 


The revolving electrons in the molecules of a per¬ 
manent magnet form ampere-turns which give the mag¬ 
netizing force utilized to make other magnets by the 
stroking method. See Fig. 49. 

Effect of Breaking a Magnet. —Since every tiny 
particle of the iron is a magnet and has two poles of 


A 




Fig. 56. Breaking Magnets. 


opposite polarity, the effect of breaking a magnet should 
be to produce two magnets. This is exactly what hap¬ 
pens. Fig. 56 A is a picture of what actually happened 
when a magnet was broken. 

Experiment 36.—A test tube filled with iron filings 
when placed in a solenoid becomes a magnet. If care¬ 
fully handled it holds some of the magnetism, but when 
shaken all the little magnets get jumbled up and their 
polarities cancel. Fig. 56 B shows how to arrange the 
filings in the test tube. 

Magnetic Field. —The space throughout which 
the magnetic force of a magnet can be detected is called 
the field of that magnet. 

All magnetic substances become magnetized when 
in a magnetic field. We say the magnetism is induced 
in these materials and the process is called magnetic 
induction. 














204 THE BOYS’ BOOK OF ELECTRICITY 


Magnetic Induction. —Experiment 37.—Arrange 
a magnet, a strip of wood and a piece of soft iron as 
shown in Fig. 57. The magnetic field of the magnet, 
passing through the soft iron, makes it a magnet and 



it will attract iron filings. Notice that the soft iron 
and the magnet are not in contact and that the wood 
is a non-magnetic material. 

Experiment 38.—Suspend some small pieces of 
soft iron, such as tacks, from a magnet pole. Then, as 



Fig. 58. When Two Poles Make no Polarity. 


shown in Fig. 58, place another magnet over the first 
one. Arrange the poles in the position shown. 

Now slowly push the top magnet along. As the two 
opposite poles approach, the tacks will fall off. You 





MAGNETISM 


205 


have neutralized the polarity of these poles and thus 
destroyed the magnetic field. The tacks are no longer 
magnetized and will not attract each other nor the big 
magnet. 

Perhaps you would rather have me say that the big 
magnet no longer attracts the tacks. The action is a 



mutual one, for each attracts the other. A magnet only 
attracts iron or steel by first magnetizing it by induc¬ 
tion, and then the two magnets attract each other. 

Experiment 39.—An experiment which shows the 
lifting power of a magnet due to its magnetic field is 
shown in Fig. 59. 

Arrange a strong horse shoe permanent or electro¬ 
magnet and a nail as shown. Place two slips of paper 
on each side of the nail, between it and the poles of 
the magnet. Thus there can be no actual contact 
between the nail and the poles. 

You will be able to suspend the nail in the air as 
shown. The string is to prevent the nail from swing¬ 
ing down against the support. Use a light string or 
thread so as not to add weight to the nail. 




















206 THE BOYS' BOOK OF ELECTRICITY 


No Insulator for Magnetism.—There are many 
materials which have low permeability; that is, do not 
conduct magnetism well, but there is nothing that re¬ 
fuses to conduct magnetism. Hence there is no in¬ 
sulator for magnetism, such as rubber is for current 
electricity. 

Magnetism goes through everything, as is shown 
very clearly by the following experiment. 

Experiment 40.—Suspend a small magnet and let it 
come to rest in the north and south position. Place 



Fig. 60 . Magnetic Transparency. 


beside it a piece of some non-magnetic material or this 
book that you are reading. 

Then as shown in Fig. 60 bring up a magnet. The 
suspended magnet will be moved. The dotted lines 
show the lines along which the magnetic action or flux 
exerts its force. 

Although you can not keep magnetism back by the 
use of insulators, you can keep it out of places where 
it is not desired by the use of conductors. I know that 
this sounds queer, but it is true. 

Side Tracking Magnetism.—When a piece of 
iron is placed in a magnetic field, the iron, due to its 











MAGNETISM 


207 


superior permeability, concentrates all the magnetic 
flux into itself. Hence the surrounding space loses 
almost all its magnetic force. 

You can practically clear a space of magnetism by 
completely surrounding it with a thick wall of soft iron. 
The iron conducts so well that the magnetism will go 



Fig. 61. Protecting a Watch from Magnetism. 

through a long path of iron, rather than a short path 
of air, brass, gold and such materials. 

If a watch is placed in a magnetic field its hair spring 
and main spring will become magnetized and the watch 
will not keep correct time. 

Protecting Watches. —Enclosing the watch in a 
soft iron case protects the watch by side tracking the 
magnetism, as in Fig. 61. The magnetism will go 
through the iron case and thus around the watch. There 
will be no magnetic field inside the case, although the 
iron case be as thin as a 64th of an inch. 

Experiment 41.—Arrange a suspended magnet and 
a thick plate of magnetic material, the thicker the better. 
The permeability should be high, so iron is better than 
steel. I suggest a laundry iron, waffle iron, or griddle 
as handy things. When the magnet is brought up the 


208 THE BOYS’ BOOK OF ELECTRICITY 


flux passes through the iron but not across it and out 
into the air. So the suspended magnet is not affected. 
Fig. 62 shows the path of the magnetic flux. Hence 



Fig. 62. Shielding from Magnetism. 


there is no magnetic field beyond the iron coming from 
the magnet. 

The Compass.—The practical use of a freely 
suspended magnet as a guide in navigation is greatly 
interfered with by the fact that the compass does not 
point to the true north. 

The suspended needle does not point to the spot 
where the earth’s axis passes through the surface of 
the earth, but to a point to the south of this. 

The magnetic north pole is in the Boothia Peninsula 
of the Dominion of Canada, 1300 miles south of the 
earth’s north pole and directly north of the central part 
of the United States. 

Declination. —The declination of the needle is the 
angle between the indication of the compass and the 
line to the true north. 

There are agonic lines or lines of no variation on the 
earth's surface, along which the compass points to both 









MAGNETISM 


209 


the north magnetic and geographic poles. At all other 
places the indication of the compass must be corrected 
to obtain the direction of the north pole. 

The simplest form of compass is a light magnet 
floated .upon a cork. The magnet will turn into a 
magnetic north and south position. See Fig. 63A. 

Dip .—Experiment 42. — Arrange two steel knitting 
needles as shown in Fig. 63 B. The cylindrical needle 
on the edges of the glasses causes very little friction. 



Adjust the position of the needle until you have an 
exact balance. Then without disturbing the position 
of the needles magnetize the one not used as an axle. 
Upon replacing them on the glasses the balance will be 
destroyed. In New York the north end will dip and 
the magnetized needle take the position shown in Fig. 
63 B. The angle between the needle and the horizontal 
plane will be 70°. 

In the Southern hemisphere the south end of the 
needle will dip. 

The Earth a Magnet. —The declination and dip 
of the needle are due to the earth acting like a huge 








2 io THE BOYS’ BOOK OF ELECTRICITY 


magnet, with two opposite poles. A large steel ball 
when magnetized will act on a tiny compass exactly as 
our earth acts on our compasses. 

Current Acts Magnetically.—A straight wire 
carrying a current has an effect upon a magnet, which 
you will remember better if you see its results. 


The Effect of Current on a Magnet. — Experi¬ 
ment 43.—In a basin of water float a magnet on a cork. 



Fig. 64. Effect of Current on a Magnet. 


When it has swung into the north and south line, bring 
a wire carrying current directly over it. The wire is 
to be attached to the battery as indicated in Fig. 64. 
Now the current (not the electrons) flows from the 
south to the north and over the magnet. You will find 
that the north end of the magnet swings towards the 
west. 

Snow Rule. —To remember this action between a 
current and a magnet use the word SNOW. This word 
is taken from the sentence: “When the current flows 










MAGNETISM 


211 


from the South to the North Over a magnet the north 
end swings to the West.” 

Principle of the Galvanometer.—A consideration 
of the action in Experiment 43 will show you that if a 
wire carrying current is carried over and under a mag¬ 
net, it will be urged in the same direction by each part 
of the current. For the current flowing to the north 
and over the magnet twists it in the same direction as a 



Fig. 65. Principle of the Galvanometer. 

current in the opposite direction on the opposite side, 
that is, under the magnet. See Fig. 65. 

Weak currents may make a strong effect on a mag¬ 
net if many turns of wire are wound into a coil and the 
magnet suspended in the coil. For the exact arrange¬ 
ment see Fig. 7. 

Further Experimentation.—With a few magnets, 
both permanent and electromagnetic types, needles, iron 
filings and a sheet of cardboard any ingenious boy will 
have lots of fun. More than that, you will find out 
what can and can’t be done with magnets. Beware of 
saying that something can not be done until you try it. 

You would not think that a. c. would magnetize a 
horse shoe electromagnet. If you have a. c. in your 
home, use the 110 volt control panel to attach the 
magnet to the supply. You will find that the magnet 
will support weights. The poles are continually chang¬ 
ing, but any pole will attract magnetic substances. 







CHAPTER X 

DYNAMOS, MOTORS AND TRANSFORMERS 


Electromagnetic Induction 
Inducing Current 
Experiment 44 

Rule eor Direction oe Induced Currents 
Facts About Induced Currents 
A Simple Alternator 
A Simple Direct Current Generator 
The Commutator 
The Armature 
Armature Cores 
The Fields 

The Voltage oe a Dynamo 
Voltage Regulation in A Power Plant 
Current Capacity 
Motors 

What Makes a Motor Go 
The Work of the Commutator 
The Power oe a Motor 
Rule for Power 
Rule for Speed 
Rating of a Motor 
Output 
Intake 
Efficiency- 
Current Taken 
Shunt Motors 
Series Motors 
A. C. Motors 
Series Motors Again 
The Universal Motor 
Induction Motors 
Reversing a Motor 
Boosters 
Dynamotors 

Motor-dynamos 

Rotary Converter 


213 


214 THE BOYS’ BOOK OF ELECTRICITY 


A Dissected Dynamo 
The Transformer 
Experiment 45 

How a Transformer Works 
Small Transformers 
Commercial Transformers 
The Induction Motor 
•Polyphase A. C. 

Pole Changing Switch 
Commutating Switch 


CHAPTER X 


DYNAMOS, MOTORS, AND TRANS¬ 
FORMERS 

Dry cells, wet cells, storage batteries and all such 
devices for sending out streams of electrons are too 
small to be used as commercial sources of power. 

If the water supply for your home were delivered 
daily in buckets you would be unable to lead a modern 
life. In a similar way the widespread use of electricity 
in our daily life is made possible only because we have 
electricity at the turn of a switch, just like water at 
a faucet. 

To properly and economically operate the many elec- 
1 trical appliances in our homes, offices and factories we 
need lots of electrons at high pressure. Cells will not 
do. We must utilize the principle of 

Electromagnetic Induction. —When a magnetic 
field and a conductor move toward or away from each 
other there is produced in the conductor a force that 
moves electrons. 

This relative motion of the field and the conductor 
may be accomplished in several ways. 

1. In very high voltage a. c. generators the magnetic 
field is moved and the conductors are stationary. 

2. In d. c. generators the conductors are moved, 
while the magnetic field remains at rest. 

This is because the electrical engineer has found it 
better to design the a. c. and d. c. dynamos, or gen¬ 
erators, as they are usually called, in these ways. It is 
not because the different ways produce different kinds 
of current 


215 


216 THE BOYS’ BOOK OF ELECTRICITY 


Before you can understand the action of a generator 
you must firmly fix these truths in your mind. 

1. Motion that carries a conductor across a flux 
produces current in the conductor. 

2. The direction of the current depends upon the 
polarity of the flux cut and the direction of the motion 
of the conductor across this flux. 

I am speaking of flux as if a definite something 
flowed from the north pole to the south pole of a magnet. 
Perhaps nothing does, but the process of electro¬ 
magnetic induction acts as if something was cut by the 
passing of the conductor across it. 

Let us get our ideas straightened out by performing 
this experiment. 

Inducing Current. —Experiment 44. —Wind a 
small cardboard tube or a form about two inches 
square with 100 turns of No. 30 cotton-covered wire. 
Place it as shown in Fig. 66 in the field of an electro¬ 
magnet. Connect this coil to a galvanoscope. Be 
sure that the coils A and B, often used with this galvan¬ 
oscope, are not in the circuit. 

When you suddenly draw the coil out of the mag¬ 
netic field the galvanoscope will give a momentary de¬ 
flection. If you suddenly thrust the coil into the field 
the galvanoscope will give a momentary deflection, but 
in the opposite direction from before. The arrows in 
Fig. 66 show the direction of the current when the coil 
is thrust into the magnetic field. 

The size of the deflection depends on the speed of 
the motion. If you will now unwind half the coil and 
repeat the experiment you will find that the deflection 
is half its previous value. 

By this experiment you have learned enough to see 
that a rule might be written to predict the direction of 
the current when the circumstances are known. 


DYNAMOS, MOTORS AND TRANSFORMERS 217 


Rule for the Direction of Induced Currents.— 

Hold the thumb and first two fingers of the right 
hand so that the thumb, the first and the middle fingers 



Fig. 66. How Current is Produced by Magnetic Induction. 

are at right angles to each other. Fig. 67 shows ex¬ 
actly how to do it. 

Let the first finger point from the north pole to 
the south pole of the magnet, that is in the direction 
of the flux. Let the thumb point in the direction of 
the motion of the conductor. Then the center finger 
will point in the direction of the induced current. 

Memorizing this rule is made easy by fixing the 
mind on First finger for the flux and Center finger 
for the current. 

Should you want a rule for the flow of the electrons, 
then use the same rule with your left hand. 



























218 THE BOYS’ BOOK OF ELECTRICITY 


The apparatus shown in Fig. 66 may be used to 
show the following. 

Facts About Induced Currents. — 1 . When a wire 
moves in a circle, cutting through the flux between two 
magnet poles, the induced current is reversed twice a 


SOUTH 

POLE 





H/RT MOWMG 
UPWARDS 

U-X _*_ 


WORTH 


POLE 


Fig. 67. Right-hand Rule for Induced Current. 

revolution. The current generated is an alternating 
current. 

2 . The swifter the movement of the wire the greater 
the current. 

3. The stronger the magnetic field the stronger the 
current. 

A Simple Alternator. —The alternating current 
generator or dynamo is usually called an alternator. 
In its simplest form it consists of a field magnet and 
an armature. The armature consists of the winding and 
the core. The core is of soft iron, thus making the 
path, for the flux from pole to pole of the field magnet, 
more permeable. 

To make the picture clearer, in Fig. 68 we have 
























DYNAMOS, MOTORS AND TRANSFORMERS 219 


omitted the core on which the wire of the winding is 
wound and have shown but one coil of wire of the 
winding. But since every wire does the same thing 
and has the same things happen to it, one wire will be 
enough for our explanation. 

The situation shown in Fig. 68 is that of the wire 



on the left hand side of the winding having just com¬ 
pleted a passage across the face of a north pole. 

By remembering our right hand rule we could pre¬ 
dict that a current would be flowing along this wire 
in the direction shown by the arrow. 

On the right hand side of the armature is a wire that 
has just passed across or cut, as we say, the flux enter¬ 
ing the south pole. 

























220 THE BOYS’ BOOK OF ELECTRICITY 


Remembering that the flux is said to flow from the 
north pole to the south pole, by using the right hand 
rule, we expect the current to flow in the direction of 
the arrow. 

Considering the two wires as a loop you will see 
that the current tends to flow around this loop. 

If two cylinders of copper are mounted on the axle 
of the armature and these two cylinders are insulated 
from the axle or shaft and from each other, we may use 
these as sources of current. 

To do this solder one end of the coil of wire to one 
of the cylinders or collecting rings, as they are called, 
and the other end to the other collecting ring. All as 
shown in Fig. 68. 

Arrange to have the wires of the outside circuit end 
in flat pieces of carbon or copper called brushes. 
These brushes held firmly to the frame of the generator, 
slide on the collecting rings and allow the current to 
flow out and into the alternator. 

Notice that the wire attached to a collecting ring is 
alternately going up across the flux on one side and 
then down across the flux on the other side. Thus 
this collecting ring is alternately sending electrons out 
of the machine and then pulling them back again. 

In such a machine as pictured here the current 
generated must be an alternating one. Since no dy¬ 
namo or generator has any different internal arrange¬ 
ment, all generators are alternating current generators. 

Don’t get excited. I mean it. A direct current 
generator is an alternating current generator with a 
built in device for reversing the connections of the 
armature to the outside circuit at the proper time, so 
that the outside circuit receives direct current. 

A Simple Direct Current Generator. —In Fig. 69 
is shown the same machine that we have been discussing 
with the collecting rings removed and a new device 
substituted for them. 


DYNAMOS, MOTORS AND TRANSFORMERS 221 


This device is called a commutator. It is really 
nothing more than a rotating switch. 

The Commutator. —In its simplest form as shown 
in Fig. 69, it consists of two copper strips or segments 
in the shape of half cylinders. These are mounted as 
shown, and insulated from each other and from the 



shaft of the armature. The coil of wire has each end 
attached to one of these commutator segments. 

The situation pictured is where the current is flowing 
out of the right hand brush. Hence this is called the 
positive brush. 

Remember that the brushes are stationary and that 
the commutator revolves with the armature and its 
windings (coils). You will observe that when the 
armature wire, now in front of the south pole, moves 




























222 THE BOYS' BOOK OF ELECTRICITY 


over in front of the north pole, and the current in it 
reverses, it will then be connected by the commutator 
to the other brush. 

In this way the a. c. generated in the armature 
winding is rectified or commutated by this rotating de¬ 
vice, so that current always flows out from one brush 
and flows in by the other. Thus the outside circuit is 
served with d. c. 

The Armature. —In actual machines, having but 
one coil on the armature would result in an uneven 



Fig. 70. Diagram of an Armature. 


or pulsating e. m. f. Hence many coils of several 
turns each are wound on the core and each is con¬ 
nected both to its neighbor and to a pair of commutator 
segments. Fig. 70 shows an armature with two coils. 
For convenience in winding, each coil was put on the 
core in two parts. 

Each coil is connected to a pair of commutator seg¬ 
ments. 

Armature Cores. —The soft iron core which sup¬ 
ports the windings has additional functions. It must 
revolve the wire through the flux against the force 
which the flux exerts to hold these windings stationary. 
Hence these cores are slotted, and the armature coils 



DYNAMOS, MOTORS AND TRANSFORMERS 


223 


are wound in these slots. It must also furnish a very 
permeable path for the flux from pole to pole. Hence 
it is of very soft iron. 

But this is not all. The core is not only magnetized 
by the fields but as the core revolves its magnetic 
polarity is continually reversing. To prevent exces¬ 
sive heating under these circumstances the core is made 
of sheets of soft iron. We say that the cores are 
laminated. 

The Fields. —The magnets producing the magnetic 
flux of a generator are called field magnets or simply 
the fields. Note that the alternator requires direct 
current in the coils of its field magnets, just as a d. c. 
generator does. 

The field current for an alternator is supplied by a 
separate d. c. generator or from a commutator mounted 
on its own shaft which rectifies enough current to serve 
the field magnets. 

•In d. c. generators, two wires lead from the brushes 
to the field coils. This type of generator is called a 
shunt generator to distinguish it from the very rare 
type called the series. In this latter type all the cur¬ 
rent going through the external circuit also passes 
through the fields. 

The Shunt Dynamo. —The shunt generator tends to 
give a steady e. m. f. because the current flowing in 
the main or external circuit has very little influence 
on the current in the field circuit. Each is supplied 
by the e. m. f. of the machine, but they are separate, 
independent circuits. Fig. 71 shows the electrical con¬ 
nections of a shunt generator. 

The Voltage of a Dynamo.—The e. m. f. of a 
dynamo depends on the number of turns of wire on 
the armature that are connected in series, on the speed 
with which these wires cut the flux and on the quantity 
of flux, that is the strength of the magnetic field. In¬ 
creasing any one of these increases the e. m. f. 


224 THE BOYS’ BOOK OF ELECTRICITY 


Since the armature winding offers some resistance, 
as soon as the dynamo delivers current there will be a 
drop in the armature winding and the voltage at the 
terminals of the dynamo will be less than its e. m. f. 

Voltage Regulation in Power Plants. —To keep 
the voltage up to the proper value a rheostat is used 



Fig. 71. Diagram of Connections of a Shunt Dynamo. 

in field circuit. This resistance is cut out of the cir¬ 
cuit, by the man in charge of the dynamo, a little at a 
time, so that although the drop increases with the load, 
the increased field strength will keep the voltage con¬ 
stant. 

Current Capacity. —An armature wound with 
small wire cannot carry a heavy current without over¬ 
heating. The current capacity is thus determined by 

















DYNAMOS, MOTORS AND TRANSFORMERS 225 

the current the armature can carry with an increase 
of temperature of not over 90° Fahr. It has been 
found that it is not safe to operate a dynamo at a 
temperature higher than 175° Fahr. 

Remember that you may draw any current you 
please from a dynamo. The e. m. f. is fixed by the 
design of the machine but you regulate the current by 
changing the external resistance. Every time you turn 
on a lamp or a toaster, since they are in parallel, you 
are lowering the resistance of the circuit and thus the 
e. m. f. is able to produce a greater current. 

Our demands for current from a certain dynamo 
must be regulated by the knowledge that too much 
current will burn the insulation from the wire on the 
armature, and thus cause need for an expensive repair. 

Motors. —We have seen that like poles repel 
and unlike poles attract each other. This force is in¬ 
creased as the strength of the poles increases. 

If we could arrange one magnet on a pivot between 
the poles of a stationary magnet the pivoted magnet 
would turn until the poles were in a straight line. 

Suppose the dynamo shown in Fig. 69 is connected 
to a d. c. source of power. The armature would make 
half a revolution and then stop. There is a way of 
winding an armature so that it will make a complete 
revolution and keep on revolving as long as it is served 
with electrical power. 

Wind the armature with two coils at right angles to 
each other. Connect these coils to commutator seg¬ 
ments as shown in Fig. 72. 

If the machine is in the position shown in the illus¬ 
tration, the current will enter through the -f- brush to 
commutator segment C, thence into coil 1 on the arma¬ 
ture. Passing through the turns of this coil the cur¬ 
rent will leave by commutator segment D and the 
brush back to the source of power. At the same time 
the field coils have been excited, as we say, and we 


226 THE BOYS' BOOK OF ELECTRICITY 


have on the field magnets north and south poles as 
indicated. 

Coil 1 makes the soft iron core of the armature 
upon which it is wound, a magnet. Now the ends of 
the hole about which a coil of wire is wrapped are the 



magnetic poles due to that coil. When that hole is 
filled with a core which projects out of the coil, then 
the poles move out on the core towards the ends of the 
core. This is shown in Fig. 73 where you see the 
position of the poles of a solenoid, and where they 
are on a magnet like a field magnet of a dynamo or 
motor. 

There is also shown how, on an armature core, the 
poles are on the sides of the core, because the sides 






































DYNAMOS, MOTORS AND TRANSFORMERS 227 

of the core are also the ends of the hole inside the 
coil. 

If you will now return to Fig. 72 you will under¬ 
stand why current through Coil No. 1 produces mag¬ 
netic poles on the armature core at N and S. 

W hat Makes a Motor Go.—T hings being as they 
are pictured in the illustration the armature will re¬ 
volve in the direction shown by the arrow until the 
armature and field poles are opposite to each other. 
We can rely on the momentum of the moving armature 
to carry it around so that the N and S poles will ar¬ 
rive at the places marked B and A. Then all tendency 
to revolve ceases. 

The Work of the Commutator. —Let us not for¬ 
get that the commutator is fastened to the armature 
and so turns with it. Thus by the time the poles N 
and S have arrived at B and A, commutator segments 
E and F are connected with the brushes. Hence the 
current is cut off from Coil No. 1 and flows through 
Coil No. 2. 

But Coil No. 2 is now in the place where Coil No. 1 
used to be and so Coil No. 2 places magnetic poles 
at the points marked N and S. Thus a new attraction 
is created between the field and the armature poles. 

Thus the separate coils on the armature and the 
action of the commutator continually form a north 
pole at N and as it is attracted to the south pole of the 
field magnet, they move it suddenly back to the point 
N. 

The Power of a Motor. —To make a motor 
powerful we wind the armature with many small coils 
connected to as many pairs of commutator segments. 
We permit each coil to form the magnetic poles only 
when it is in the most advantageous position. We also 
make the field flux as large as possible. 

Rule for Power. —The product of the field and 
armature magnetisms indicates the power of the motor. 


228 THE BOYS* BOOK OF ELECTRICITY 


Rule for Speed. —The stronger the armature mag¬ 
netism the faster the speed, the weaker the field mag¬ 
netism the faster the speed. 

Rating of a Motor. —The amount of horse power 



AN ELECTROMAGNET 



AN ARMATURE 


Fig. 73. Poles of a Solenoid and a Magnet. 

that a motor can deliver depends on how hot it gets 
due to i 2 r losses while it is working. 

The horse power which it can deliver continuously 
without getting hotter than 175° Fahr. is the rating 
of the motor. 

if you buy a % H. P. motor and while delivering 

















DYNAMOS, MOTORS AND TRANSFORMERS 229 


full rated power it heats up to 200° Fahr., then that 
manufacturer was too optimistic. You would not be 
wise to so load it. Motors are supposed to be capable 
of standing a 25% overload for 3 hours with no 
damage to the machine. 

Output. —A % H. P. motor is rated on its output. 
Due to losses it will take more than Ys H. P. from the 
line. 

Intake. —Since 746 watts are equivalent to 1 horse 
power, the Ys H. P. motor must take 746 x 34 or 93.3 
watts from the line at 100% efficiency. 

Efficiency. —Dividing the output by the intake 
gives the efficiency, when of course both are expressed 
in the same units. Hence knowing the output we divide 
it by the efficiency to get the intake. 

Remember that in all problems efficiency is expressed 
as a decimal fraction not as a percentage. 

The Yg H. P. motor gives out 93.3 watts. At 70% 
efficiency it must have an intake of, 93.3 -f- .70 which 
is 137.7 watts. 

Current Taken. —The current needed to supply 
137.7 watts will depend on the voltage of the supply 
lines. 

Since watts are figured by the product of the am- 
peres and the volts, then the watts divided by the volts 
will give the amperes. Thus 137.7 watts delivered at 
110 volts requires a current of 137.7-r-110 or 1.25 
amperes. 

Shunt Motors.—The motor that was described 
so fully and the diagram of its connections given in 
Fig. 72 was a shunt motor. This name shows that 
the armature and field circuit are shunts on the main 
or external circuit. Fig. 74 may show this more 
clearly. 

The tendency of a shunt motor is to operate at a 
steady speed. For this reason it is the best motor 
for use in factories to drive machinery. 


230 THE BOYS’ BOOK OF ELECTRICITY 


Series Motor. —When the armature and the field 
coils are in series, we have a motor willing to move 
at any speed and very powerful at low speeds. These 
two qualities make it very valuable for traction, mean- 


supply 


SUPPLY 



P/ELD 

-WVWVAAAAA/^ 



-VWWVWAr- 

P/SLO 

SHUNT YY/ND JNG 


Fig. 74. Hook-ups for Shunt 



and Series Motors. 


ing electric railway use, and for hoists and elevators. 
For the connections see Fig. 74 . 

A. C. Motors. — I have assumed that only d. c. 
was to be used in the two motors that I have described. 

If the field of a shunt motor is separately excited, 
as in the a. c. generator, and its armature served with 
a. c. the motor is called a synchronous motor. This 
motor when once started runs at exactly the same 
speed electrically as the generator in the power house 
which furnishes the power for it. 

By that statement I mean that motor and generator 
armatures pass by the same number of pole pieces 
per second. Hence an 8 pole motor driven from a 6 
pole generator would run at % of the speed of the 
generator. 




















DYNAMOS, MOTORS AND TRANSFORMERS 231 


Series Motors Again. —If a series motor is served 
with a. c. all the polarities will reverse at the same 
instant. Since the rotative force is the same between 
a field and an armature pole as long as they are of 
unlike polarities, the motor operates equally well on 
d. c. and a. c. 

The Universal Motor. —For this reason vacuum 
cleaner motors, and all those sold for use over widely 
spread areas are series wound motors. The owner of 
a vacuum cleaner can move from one city to another, 
from an a. c. district to some d. c. district and the 
series motor in the cleaner functions properly in both 
places. 

Induction motors will be spoken of after the 
transformer has been explained. 

Reversing a Motor. —The talk about a series 
motor on a. c. supply lines will show you that if the 
wires leading to any motor are interchanged at the 
point of supply, all you have done is to reverse all 
the polarities throughout the motor. This of course 
will not reverse the direction of rotation of a motor. 

To reverse a motor reverse the connections of the 
armature or of the field but not of both. 

Since weakening the field increases the speed, it is 
dangerous to open the field circuit of a motor while 
it is running. Do not arrange any switch that might 
open the field circuit at the wrong time and have all 
field connections tight. 

Boosters. —When d. c. must be carried long dis¬ 
tances the inevitable drop on the line may make the 
voltage at the distant place too low. Rather than raise 
the voltage at the power house we may boost it at the 
end of the line. 

This is done by placing the armature of a series 
dynamo in the line and thus by its action adding a few 
volts of pressure. This can be driven by a motor 


232 THE BOYS' BOOK OF ELECTRICITY 


attached to the same supply lines that the booster is 
boosting. 

Dynamotors. —By a clever method of winding 
the motor and dynamo coils may be on the same arma¬ 
ture. Then one machine is a motor and a dynamo at 
once. These are called motor-dynamos or dynamotors. 

These machines sometimes are attached to 110 volt 
lines and draw, say 100 amperes, but deliver 1000 
amperes at 10 volts for use in the electro-refining of 
metals. 

Rotary Converter. —When a dynamotor takes 
the supply for the motor from a. c. lines and delivers 
d. c. from its dynamo winding it is called a rotary con¬ 
verter. These must be used when the supply is a. c. 
and the work like electro-plating must be done by d. c., 
or any other place where d. c. is essential for operation 
and the current needed is large. 

A Dissected Dynamo.— So that you may learn 
the names of the parts of a dynamo or motor, in 
Fig. 75 there is shown a d. c. dynamo taken apart. 
A d. c. motor or a universal motor would have exactly 
the same appearance. 

Upon a shaft A is mounted a core on which the 
windings are placed. The part B is the part of the 
armature where the slots in the core are filled with 
the armature windings. This part passes before the 
pole faces N. 

The commutator D is mounted far enough from B, 
that the ends of the windings may be bent around 
from slot to slot, and the ends of the coils formed by 
the windings may be brought to the commutator for 
soldering to its segments or bars. 

The wires at C are not active in producing pres¬ 
sure. They are usually bound with tape and canvas 
to reduce friction as the armature revolves rapidly. 

Bearings like E, with rings to carry oil up for their 
lubrication, are set in the pillow blocks F and F. The 


'WjllhlB 


DYNAMOS, MOTORS AND TRANSFORMERS 233 



Fig. 75 . The Parts of a Dynamo or Motor. 






























234 THE BOYS’ BOOK OF ELECTRICITY 


shaft A goes through the hole in the bearing E. The 
cap G holds the bearing E firmly in F. 

The yoke or field ring H and K carry the field or 
magnet cores N. The field coils M when in place are 
held by the pole pieces screwed on N. 

The lower part of the yoke K and the two pillow 
blocks are supported by the bed plate L. 

The brush holders with their brushes P are held in 
a ring O so pivoted that the position of the brushes 
on the commutator can be adjusted. A bolt through S 
holds the ring O to the adjusting mechanism. R is the 
insulated handle by which the brush ring O is moved. 

From the brush holders cables or heavy conductors 
Q lead to a terminal block or lug on the frame or yoke. 

On the shaft a pully T is fixed by a wedge or as 
it is called a key U. 

Putting these parts together in the factory is called 
the assembling of the dynamo. Putting it on its foun¬ 
dation in the power station is called the installing or 
setting up. 

The Transformer.—When the voltage of an a. c. 
line is to be boosted or lowered, thanks to the principle 
of electromagnetic induction, it can be done by a device 
that does not contain mechanically moving parts. 

We have learned that any motion of a wire across 
a flux or a flux across a wire produces current. That 
the e. m. f. of the current depends on the number 
of turns of wire and the strength of the flux. Let 
us review these facts by an experiment. 

Experiment 45 .—At one end of a bar of soft iron 
or a bundle of soft iron wires, about 5 inches long 
and an inch in diameter, wind a coil of 20 turns of 
insulated wire. On the other end wind 10 turns of 
wire and do not cut the remainder of your wire off. 

Arrange a set-up as shown by the hook-up of Fig. 
76 . A indicates a six volt storage battery or 3 dry 


DYNAMOS, MOTORS AND TRANSFORMERS 235 

cells arranged in series. S is a pole-changing 
D. P. D. T. switch, details of which are given at the 
end of this chapter. B is the iron bar. P is the primary 
coil of 20 turns. S is the secondary coil of 10 turns. 
G is the galvanoscope. At one of the binding posts 
of the galvanoscope, scrape the insulation from the 
wire and loop the wire on the post. Do not cut off 



Fig. 76 . Principle of the Transformer. 


the surplus wire but let it remain in a coil or spool 
at D. 

The force that will act to deflect the galvanoscope 
will be a weak one, for you have a small amount of 
power at your disposal. Hence you must use the 
astatic needle magnet system in the galvanoscope. 

Try the experiment just as described and when fully 
familiar with it, replace A with the cap G from the 
110 volt control panel shown in Fig. 44. You may 
then get much a larger current in the primary P. 

Throw the switch S to one side and notice the 
kick or momentary deflection of the galvanoscope. 
Throw the switch to the other side thus reversing the 
direction of the current and the kick of the galvanoscope 
will be in the opposite direction. 

Thus by an alternating current you have through 
the magnetic flux of the bar produced an a. c. in the 
secondary coil. 

Remove the wire from the binding post C and wind 
10 turns more on the bar. Again scrape a little in¬ 
sulation and loop the wire under C. 

Repeat the experiment obtaining larger deflections. 
Then wind on over the 20 turns, 20 more making 40 










236 THE BOYS’ BOOK OF ELECTRICITY 


in all and repeat the experiment. The more turns on 
the secondary coil the larger the kick of the galvano- 
scope’s pointer. 

How a Transformer Works.—When two coils 
are wound on a soft iron core, thoroughly insulated 
from each other and from the core, you have a trans¬ 
former. 

Supply one coil with a. c. and the rise and fall in 
the strength of the flux will produce a. c. in the other. 
The one fed with a. c. is called the primary and the 
one in which the a. c. current is induced is called the 
secondary. 

The power in the secondary is produced by the 
flux being moved across the wires of the secondary 
winding. 

To calculate the voltage of the secondary, the primary 
voltage is multiplied by the quotient obtained by 
dividing the number of turns of wire in the secondary 
by the number of turns of wire in the primary. 

The current in the secondary is obtained by multiply¬ 
ing the primary current by the primary voltage and 
by the efficiency expressed as a decimal, then divide 
by the secondary voltage. 

Small Transformers. —In Fig. 6 is shown a small 
transformer used to operate toys and miniature elec¬ 
trical railways. Small transformers like this but not 
adjustable for the voltage of the output are used as bell 
ringing transformers. These are connected to the 110 
volt house supply and furnish 6 volts as an e. m. f. 
to operate the door and call bells of a building. 

Commercial Transformers. —In large cities these 
transformers are buried in brick chambers under the 
streets or in little vaults in the cellars of hotels and 
apartment houses. In the suburban districts they are 
to be seen on poles or up near the eaves of the build¬ 
ings. 


DYNAMOS, MOTORS AND TRANSFORMERS 237 

As pictured in Fig. 77 there are two wires carrying 
high voltage a. c. entering the transformer. The two 
wires leaving it are at a lower voltage but carrying 



Fig. 77. The Commercial Transformer. 

more amperes. This type is called a step down trans¬ 
former. 

The interior view shows the soft iron core and how 
the primary and secondary are each wound in two 
sections. The direction of the flow of the flux is shown 
in dotted lines. 

If you will picture the actual magnetism as a some¬ 
thing at right angles to these dotted lines and moving 














































238 THE BOYS’ BOOK OF ELECTRICITY 

around the magnetic circuit, then you will see that 
this magnetism would cut across the wires of the sec¬ 
ondary winding. 

Lay your pencil along the line A B and move it 
around back to its original position. If this was the 
flux it would be doing the things that we say flux does. 

The Induction Motor.—Suppose a motor was 
almost ready to leave the factory. The brushes and the 
connection between field and armature were not yet 
installed. 

Just as the machine stood it would be a sort of a 
transformer, with one part revolvable. Although there 
is no electrical connection to the armature there is a 
magnetic connection by means of the field flux. 

If now we connect a polyphase a. c. supply to the 
field there will be generated in the armature, by a 
transformer action, a current. This current will cause 
the armature to revolve and we have a motor. Such a 
motor, when properly wound so as to run efficiently 
in this way, is called an induction motor. 

Polyphase A. C.—Ordinary a. c. is single phase. 
When two or three single phase currents are sent 
through a set of two or three wires the combination is 
called two-phase or three-phase or simply poly-phase, 
which means many phase. This is “deep stuff,” so 
let us leave it for another book. 

Pole-changing Switch.—In Experiment 45 there 
was shown in a diagrammatic way a pole-changing 
switch which I would like to explain more in detail. 

A switch of the D. P. D. T. type is wired as shown 
in Fig. 78 using insulated wires. The double-pole 
double-throw switch shown has convenient set screws. 
Should your switch have lugs the wires should be 
soldered into these lugs. 

If this switch is closed by throwing the handle to 
the right, the current flows directly out and the wire 
C is positive while D is negative. Throwing the handle 


DYNAMOS, MOTORS AND TRANSFORMERS 239 

to the left by means of the cross over wires makes 
C negative and D positive. 

Go over the circuits in Fig. 78 carefully. The 
switch is shown almost closed, close it and the cur¬ 
rent from A flows to C, making C positive. 

When the switch is thrown to the left, the current 
flows from A to E, then to D making D positive. 



Fig. 78 . A Pole-Changing Switch. 


Commutating Switch.—I always liked to make 
things myself and so preferred another type of pole¬ 
changing switch. This latter type is usually called a 
commutating switch but is merely a pole changer. 

In Fig. 79 you may follow the details as they are 
described. The base block is drilled half way through 
at four places and four binding posts A, B, C and D 
mounted near them. From each binding post an iron 
wire goes over to the hole which is filled with mercury. 
You must use iron wire, for otherwise the mercury 
would dissolve the end which dipped into it. 

The jumper is made from heavy iron wires, or 
several twisted together and inserted in a small wooden 
block as shown at J and K. 

The operation of this device reverses the polarity of 
the current going to the experiment. 









240 THE BOYS’ BOOK OF ELECTRICITY 


Let the jumper board be so placed that J connects 
E and F and K connects H and G. Then D becomes 
the same polarity as A. If the jumper board is lifted, 
rotated a quarter of a circle and set down, then E 



would be connected to H and G to F. This would 
make D the same polarity as B. 

This simple device, easily made with your tools, is 
as good as the pole-changing switch the main part of 
which you would be compelled to purchase. 










CHAPTER XI 

FAMILIAR THINGS 

The Electric Bell 
The Push Button 
The Vibrator 
Bell Troubles 

Multiple Control oe Bells 
Group Control 
Two Way Communication 
The Buzzer Telegraph 
Buzzers 

Single Stroke Bells 

The Recording Watt Hour Meter 

Electric Lighting 

Blackening of Bulbs 
Smashing Point 
Nitrogen Lamps 
Staircase Lighting 
The Electric Iron 
The Electric Fan 
Speed Regulation 
Starting a Motor 
Back E. M. F. 

The Electric Elevator. 

Armature Resistance 
Starting Boxes 

Electrical Connections 
The Telegraph 
The Key 
The Sounder 
The Circuit 
The Telephone 
Sound 

The Transmitter 
The Receiver 

How the Telephone Works 

241 


242 THE BOYS’ BOOK OF ELECTRICITY 


The Induction Coii, 

Its Action 

Experiment 46 
The Vibrator 
The Condenser 
Uses of the Induction Coil 
Ignition 

The Make and Break Spark 
The Jump Spark 
Ford Ignition 
One Coil System 
Walking on Third Rails 
Sitting on 22,000 Volts 
Can no Volts Kill You 
How Many Volts Will Run a Motor 
What is a 50 Watt Lamp 
Where are the Abandoned Steee Ships 


CHAPTER XI 


FAMILIAR THINGS 

The Electric Bell.—First we will consider the cir¬ 
cuit which makes the operation of the bell possible. 
There is a cell ready to send out electrons from its 
negative terminal, which in a dry cell is the zinc can. 
The circuit must be complete at every point except the 
place from which we wish to ring the bell. At that 
place we insert a/push button. 

The Push Button. —As pictured in Fig. 80 the 
electrons go to a piece of brass at the top of the base 
of the push button. Above this is a flexible piece of 
brass which can be depressed by the button which 
projects through the cap. When these two make con¬ 
tact the circuit is completed, and the bell rings. 

When one stops pressing on the button the spring 
action of the upper piece of brass lifts it out of con¬ 
tact with the lower one and the bell stops ringing. 

The mechanism which keeps the bell ringing con¬ 
tinuously as long as the push button is pressed on is 
simple, yet very ingenious. 

The Vibrator. —The electrons entering the bell at 
B go on a wire to C. Here a post projecting from 
the frame of the bell supports a flat but bent spring, 
shown at E. This spring supports a bar of soft iron 
D which is called an armature. 

When the electromagnet G is not magnetized the 
spring E draws the armature away from the magnet 
and presses the lower end of itself against a screw F. 
We can adjust the amount by which this screw projects 
from its support and lock this adjustment. There is a 
243 


244 THE BOYS' BOOK OF ELECTRICITY 


lock nut for clamping the screw, so that vibrations 
will not move it. 

The electrons travel along the spring E to the screw 



Fig. 80. The Electric Bell. 


F and thence along the winding of the electromagnet 
G, up to the binding post A and back to the cell. 

Remember that I am talking about the flow of the 
electrons. Were I talking about current the arrow in 
Fig. 80 would point in the opposite direction. 




















FAMILIAR THINGS 


245 


Look carefully at Fig. 80 and you will see that 
where the circuit is completed G becomes a magnet and 
the armature D is attracted to the magnet making the 
attached hammer H hit the bell or gong K, so we 
hear a ting. 

But as soon as the armature moves over far 
enough to ensure a stroke of the hammer on the gong, 
the spring E moves out of contact with the screw F. 
This breaks the circuit. 

When the circuit is broken, G is no longer a magnet, 
for no electrons flow through its windings. Then the 
part of the spring near C pulls the armature away 
from the demagnetized cores of G. 

This action brings the lower end of spring E again 
into contact with F, the magnet becomes energized. D 
is again attracted and again the bell rings a ting. 

In fact the bell goes on merrily ting-a-linging as 
long as some one leans against the button of the push 
button. 

_ This comes very near to being perfectly simple and 
simply perfect. All the troubles we have with bells 
seem to be due to cheap bells and once in a while due 
to a cheap push button. If the cell wears out, please 
I do not say that the bell is out of order. If the wires 
are long and you have purchased a good bell, use two 
I cells in series. 

Bell Troubles. —When a bell ceases to ring, first 
;look at the lock nut on the screw F. Should it be 
i loose, adjust the screw F until the bell rings nicely 
and lock the nut tightly. Look for loose connections 
at all binding posts. Then go to the battery. 

There is no' convenient way of testing cells. They 
have a nasty way of keeping up appearances, showing 
a very commendable spirit, by giving full voltage, but 
|yet not being able to send enough electrons to tickle 
the bell, much less make it ring. 

Please do not laugh. The way to test cells is to 





246 THE BOYS’ BOOK OF ELECTRICITY 

buy new) ones and place them in service. If now the 
bell operates properly it proves that the old cells were 
no good. If you find the new cells do not make the 
bell work, then find the trouble and put the new cells 
in parallel with the old ones. You will get full service 
out of both sets of cells. 

Two rows in parallel, each row containing two cells 
in series, which makes four cells in use, will give more 
than twice the hours of service than only two cells in 



series. This is because in the parallel arrangement the 
cells work at a slower rate. 

Multiple Control of Bells. —We often want to 
ring a single bell from many places. This is accom¬ 
plished by wiring according to the diagram in Fig. 81. 
Any one of the push buttons will close a circuit causing 
the bell to ring. If two push buttons are operated at 
the same time the bell rings just the same. Notice that 
in this hook-up the bell and the cells are close to¬ 
gether. 

Group Control. —When we want to ring bells at 
different places at the same time we arrange them as in 
Fig. 82. Notice that a push button and its battery of 
cells are close together. No current can flow to any 
bell from any set of cells in Fig. 82 until a push button 
is operated. 

In connecting the cells to the circuit, be sure that 








FAMILIAR THINGS 


247 


the carbon or positive terminal of each set is connected 
to the same bell wire. By bell wire I mean, wire lead¬ 
ing to the group of bells. If you do not take this 
precaution, when two push buttons are operated at the 



same time, you might place equal and opposite voltages 
on the bell wires and so send no current to ring them. 

Two Way Communication. —The wiring diagram 
in Fig. 83 provides a way for Sam to signal to Bill 


F~ 





1 an 

3/ 

az 


1 

f' 




“i 


Fig. 83. Two Way Call Bell System. 


and know that the bell in Bill’s room probably rang. 
For when PI is operated the cells Cl cause both bells 
B1 and B2 to ring. 

Unfortunately it is possible for Bill to detach one 
wire from his bell B2. Then Sam can’t ring the bell 
B2 yet Bill can ring up Sam. 





















248 THE BOYS' BOOK OF ELECTRICITY 


This system provides for a two way communica¬ 
tion. If you installed this system from mother’s room 
to a maid’s room, then when the maid heard the bell 
ring, she could at once signal back that she had heard 
and was coming. Also the ringing of the bell in 
mother's room would be an assurance that the sys¬ 
tem was in working order. 

The Buzzer Telegraph. —If you replace the bells 
with buzzers, and the push buttons with keys, you 
could telegraph between two rooms or nearby houses. 
You would of course use the radio method of tele¬ 
graphing by the lengths of the sounds. 

This outfit is the best way for two fellows to study 
the radio code. You can dah-de-dit-dah as much as 
you please and not ruin the air for other listeners. 
F. b. o. m. When you become a radio ham you will 
know what that means. 

Buzzers. —When you remove the gong and the 
hammer from an electric bell you have a device that 
buzzes. This peculiar noise makes a good call signal 
and yet is not so loud as a bell. 

They are used wherever the signal will sound near 
the person wanted. Dad probably uses buzzers at the 
office. 

Single Stroke Bells. —To ring a set of signals 
such as two for one person, and three to call some one 
else, with an ordinary bell is rather a noisy operation. 

If the screw that touches the spring contact of 
an ordinary bell is turned up against the spring so as to 
make a permanent contact, we have a single stroke 
bell. This bell strikes its gong once every time a con¬ 
tact is made at the push button. 

The Recording Watt-Hour Meter. —Near the 
point where the electric supply wires enter a building a 
meter is installed. This device must register how much 
power you use and for how long you use it. 

It is a recording meter because it registers on a set 


FAMILIAR THINGS 


249 


of dials the proper numbers to enable the Service Com¬ 
pany to render the correct bill. Some meters, like 
galvanometers, ammeters and such instruments do not 
make a record as this meter does. 

It is a watt meter because the watt is the unit by 


0 / A L S 



Fig. 84 . A Kilowatt-Hour Meter. 


which power is sold. This particular type registers in 
the larger unit of 1000 watts or a kilowatt. 

It registers time because the longer the power is used, 
the longer the dials are turned and so the more the 
meter registers. 

This meter is really a small motor. The interior ar¬ 
rangements are shown in Fig. 84. 



































250 THE BOYS’ BOOK OF ELECTRICITY 

The wires which enter the building are attached to 
the heavy binding posts A and B. From A the cur¬ 
rent flows through the two series field coils and thence 
through D to the service wires of the user. Every 
ampere of current that the consumer uses goes through 
this series field and increases the speed of the motor. 

From B to C is a heavy copper strip, so that elec¬ 
trically they are the same. It is a convenience when 
connecting the wires to have two places for the two 
wires of the cable or B.X. 

Starting from C there is a circuit passing through 
the armature of the motor. If you will follow it 
through the resistance E F up to the brush G, then 
through the armature H, out of the brush K, through 
a field and down to D, it shows that this entire circuit 
is a shunt on the main line. For this reason the field 
coil in this circuit is called the shunt field. 

If the meter were changed from a 110 volt to a 220 
volt circuit the resistance E F would be replaced by 
one of greater value. This would protect the armature 
from too great a current which would overheat it. 

The shunt field is often called the starting coil for 
it is moved as close to the armature as possible with¬ 
out incurring the danger of starting the motor. Then 
when current flows the motor starts at once, for the 
friction is almost balanced by the starting coil. 

When lamps, toasters, fans and such appliances are 
in operation the current drawn by these goes through 
the series field. We then have a motor which revolves 
the faster the more current you use. 

To stop the meter promptly when the current is 
shut off, a magnetic drag is used. The permanent 
magnets act on the aluminum disk so as to form a 
dynamo, which like any dynamo resists being turned. 

This drag does not increase the size of the bill you 
receive, because that is allowed for in the calibration of 
the meter. Calibration means adjusting the speed 


FAMILIAR THINGS 


251 


so that it will correctly register the energy actually 
used. 

The moving parts rest on a jewelled bearing to re¬ 
duce friction. 

The dials show the number of kilo-watt-hours of 
energy that have passed through the meter. 

An Explanation. —I told you that shunt motors 
liked to run at a steady speed and that series motors 
were great workers at low speeds. The designer of the 
motor for this meter made it a series-shunt motor and 
so obtained the qualities, that made the change in speed 
proportional to the watts going through it. You will 
notice that in this motor the main field is in series with, 
and the armature is a shunt on the line. 

Remember when I said that the increased field 
strength lowered the speed of a motor. So it does when 
there are iron cores in the field coils, and a very small 
air gap between field and armature. But in this motor 
where there is no iron core in the armature nor fields 
and where there is an enormous air gap between them 
in comparison to an ordinary motor, the action is dif¬ 
ferent. Here increasing field strength means increas¬ 
ing speed. 

Electric Lighting. —The only practical method 
of lighting the interior of a dwelling is by the use of 
incandescent lamps. This name means that the filament 
inside the lamp is heated to incandescence, which means 
white hot. The wire does not burn up nor oxidize 
for there is no oxygen in the glass bulb. It is ex¬ 
hausted to a vacuum and sealed, or after being ex¬ 
hausted is filled with nitrogen or argon gas and sealed. 

The filament of a modern lamp is made of the metal 
tungsten, about three one thousandths of an inch in 
diameter. A long piece is strung in zigzag fashion 
on a glass support. The resistance of the filament is 
adapted to the 100 to 120 volt circuits on which the 
lamps are to be used. 


252 THE BOYS' BOOK OF ELECTRICITY 


The candle power of the lamp depends on the tem¬ 
perature, and the length of the filament. 

All vacuum bulb lamps are operated at the same 
temperature and so the length of the filament must be 
designed to have a certain resistance. Thus the cur¬ 
rent drawn by the lamp is determined, the current 
heats the filament, and we get light. 

Blackening of Bulbs. —Although the filament 
cannot burn or oxidize in the vacuum, it is heated so 
hot that it slowly boils. The metal slowly vaporizes 
and condenses on the inside of the glass bulb. Thus 
the bulb blackens and the light is weakened. 

Smashing Point. —When a bulb has become dark¬ 
ened it is cheaper to take it out and smash it, than to 
continue to use it. For you either will find yourself 
using two lamps to get the proper illumination or 
injuring your eyes. 

It costs less money to buy a new lamp than to run 
two darkened lamps. 

Nitrogen Lamps. —If the bulb after the vacuum is 
formed is filled with a gas which will not oxidize the 
filament nor permit it to burn up, we find evaporation - 
of the tungsten filament is very much retarded. 

This lamp may be designed to operate at a higher 
temperature. This makes the lamp give more light 
for less current used, which means for less money. A 
vacuum lamp requires 1*4 watts to furnish 1 candle 
power of light. A gas-filled lamp will produce the 
same light consuming only 0.8 watts. 

Staircase Lighting. —There are many places 
where two lamps or two groups of lamps ought to be 
independently controlled from two places. Staircase l 
lamps fall in this class, when duplex control is needed. 
Such a system of control is shown in Fig. 85. 

The lamp A is at the head of a stairs and lamp B at 
the foot. Switch A is upstairs and switch B down¬ 
stairs. These switches are of the familiar type where 


FAMILIAR THINGS 


253 


two buttons project in turn through a brass plate, and 
pushing the protruding button accomplishes the desired 
result. Yet they differ from the regular switches in 



Fig. 85. Duplex Control of Lamps. 

their internal connections and both buttons are of the 
same color. Any single-pole double-throw switch 
could be used. 














254 THE BOYS’ BOOK OF ELECTRICITY 


You could make a model of a system like this using 
flashlight lamps and dry cells. Then you could demon¬ 
strate to your friends exactly how such a system 
operates. 

As the switches are set in the diagram both lamps 
are lighted. To convince yourself of this, start at the 
supply lines at the point marked 1 and follow the 
circuit through the points as numbered in order. 
When you get to 13 you have completed the circuit 
that feeds lamp A. 

If you start at 14, then to 15, to 4 and then con¬ 
secutively to 13 you get the circuit feeding the lamp B. 

Suppose you had just come downstairs and wished 
to turn off both lights. Pushing the projecting button 
of switch B would open the circuit of both lamps at 
point 5. 

If you wish to ascend the stairs again, then push the 
switch back to its original position, and the lamp will 
light. 

Should you not do this but leave the switch B as 
shown in the dotted position, with the lights extin¬ 
guished, the system is ready for some one else to 
descend. 

Let them, at the head of the stairs, push switch A 
over to the dotted position and both lamps will be 
lighted. The circuit for lamp A will now be through 
the points 1, 2, 3, 17, 9, 8, 7, 6, 16, 12, 13 and similarly 
for lamp B. 

Thus the lamps can be controlled at two places. 

The Electric Iron. —This is such a convenient 
appliance that it is probably the first electrical device 
purchased by a family. 

What you want in an iron is heat. Since the heat 
produced depends on the watts converted from elec¬ 
trical energy into heat, you must purchase watts. The 
voltage of your supply being a fixed quantity, to get 
more watts you draw more amperes. 


FAMILIAR THINGS 


255 


These amperes flowing through resistance cause heat 
in proportion to the square of the amperes and to the 
ohms of resistance. Increasing the current from 1 to 2 
amperes would increase the heat to 4 times its former 
quantity. Nearly all irons draw about 5 amperes from 



the line, use power at the rate of 550 watts and cost 
from 10 to 20 cents the hour to use depending on the 
cost of power. 

The heating element of high resistance wire is shown 
in Fig. 86. This wire is wound on asbestos board and 
then mounted in the lower part of the iron. 

To disconnect the iron a removable plug is used. 
Where the flexible cord containing the supply wires 
enters this plug the bending is severe, and this is where 
the wires break. 


































































256 THE BOYS’ BOOK OE ELECTRICITY 


The Electric Fan.—Perhaps I should say at once 
that we are going to discuss the motor in an electrically 
driven fan. 

The small desk fan and the wall fan of the size 
used in homes and business offices is driven by a series 
motor. This fan may be used on d. c. or a. c. systems. 

Speed Regulation. —There are several ways of 
regulating the speed of a motor. One is by placing 
more and more resistance in the circuit which reduces 
the pressure available to run the motor, and thus re¬ 
duces the speed. Another way is to weaken the field 
by shunting turns of wire in the field winding and 
so increasing the speed. 

Starting a Motor.—When you wish to start a 
fan you push a button or snap a switch and give the 
matter no further thought. 

The resistance of the motor is sufficient to prevent 
a very large current from flowing. But should you 
hold the blades from revolving by a piece of wood 
and then turn the switch, the armature would grow 
hot and soon the insulation would be burnt. 

We know that this does not happen when the fan is 
going and so we suspect that a rotating armature draws 
less current from the line than a stationary one. An 
ammeter in the line with the armature under these two 
conditions shows a great difference in the currents. 
Please do not try this for you will surely ruin an ar¬ 
mature. 

What is it that chokes the current back when the 
armature is revolving? It is the e. m. f. that the 
motor generates as it revolves. This e. m. f. is against 
the voltage of the line and hence reduces the actual 
number of volts sending amperes through the motor. 

Back E. M F.—We call this voltage which the 
motor produces a back or counter e. m. f. When you 
realize that in a revolving motor we have all the ele¬ 
ments of a dynamo you will understand why this back 


FAMILIAR THINGS 


257 


e. m. f. is generated. In the motor in motion there 
are wires on the armature cutting the flux from the 
fields. If you cared to apply the rules of direction 
of flux, motion and induced current; and also the rules 
of the magnetic thrust on a wire in a flux, you would 
be convinced that: The voltage generated by the dy¬ 
namo action of a motor is less than and in the oppo¬ 
site direction to the voltage which makes that motor 
run. 

It is the difference between the line voltage and the 
back e. m. f. which forces current through the arma¬ 
ture. As the load on a motor increases its speed 
slackens. This makes the back e. m. f. lower, which 
in turn increases the difference between the line voltage 
and the back e. m. f. Thus a larger voltage is applied 
to the armature and more current flows to produce the 
power to move the load. 

In this way the current taken by a motor is auto¬ 
matically regulated to be just enough to do the work 
demanded of it. 

The Electric Elevator.—The elevator man moves 
a handle, and the elevator moves away from the floor 
like magic. You know in a general way that there is 
a motor down in the cellar but not perhaps much of 
how it starts and stops. 

Armature Resistance.—The resistance of the 
armature of a 10 H. P. motor such as is used in a 
decent elevator service must be very low else the power 
wasted in the armature would be too great. 

The armature of such a motor may be one thou¬ 
sandth of the resistance of a fan motor. If the voltage 
of the line were applied to the armature of this large 
motor, before it could get up enough speed to generate 
enough back e. m. f. to protect itself, the armature 
would have been badly damaged from the heat due 
to the large current flowing. 

Starting Boxes.—In order not to “burn out” 


258 THE BOYS' BOOK OF ELECTRICITY 


armatures with the heat from the first rush of current, 
a starting resistance is put in the circuit at first, and is 
cut out a little at a time as the motor gains speed. 

As this simple starting resistance is accompanied by 
other devices the whole thing is usually called a starting 
box. 

In its simplest form this consists of a lever whose 
first movement completes the field circuit. Then the 
motor cannot run at an excessive speed or race. For 
if the motor tries to go too fast the back e. m. f. will 
become so great that it will not permit enough cur¬ 
rent to flow to run the motor Thus the excessive 
speed commits suicide. 

What I have just written applies to a shunt motor 
more than a series motor, so all elevator motors have a 
shunt field winding for the special purpose of holding 
the speed down to normal. 

When the lever completes the field circuit, the next 
movement completes the armature circuit through a 
resistance. Further movement of the lever cuts out 
the resistance until full line voltage is on the motor. 

The elevator man by the handle in the car closes a 
Circuit which starts a little motor like a fan motor. 
This by a gear moves the lever of the starting box 
slowly over the contacts on the face of the box. Fig. 
87 shows a starting box. 

No Voltage Release. —If there should be a 
momentary interruption of the voltage the motor would 
stop and the return of the voltage would find an un¬ 
protected motor. It is true that some one ought to 
turn the starting box lever back to the safe starting 
point, but people forget things. 

Therefore there is an automatic device which resets 
the starting box to a safe position whenever the line 
voltage fails. This device is a spring which would 
throw the lever back to safety unless held in a position 
to run the motor by some force. 


FAMILIAR THINGS 


259 


As long as the motor is running the back e. m. f. 
of the motor magnetizes the release magnet which holds 
the lever against the action of the spring. Should the 
line voltage fail and the motor begin to slow down, 
very soon the back e. m. f. becomes so weak that the 
release magnet cannot hold the lever. Then the spring 
throws the lever back to the safe position. 

Overload Release. —If the no-voltage release coil 
was short circuited, or if a jumper or shunt were con¬ 
nected to it, it would be robbed of its current and 
hence of its magnetism. 

An overload release is a magnet with its windings 
in the armature circuit. When by reason of an over¬ 
load on the motor the current grows beyond a safe 
value, then the magnetism of this overload release be¬ 
comes strong enough to lift a bar of soft iron. This, 
by some contrivance, short circuits the no voltage re¬ 
lease, which losing its magnetism lets go of the lever 
and the spring moves it back to safety. Fig. 87 
shows a method of doing this. 

To Stop Large Motors. —Any motor provided 
with a starting box should be stopped by opening the 
main switch. The starting box is not a stopping box. 
Opening the switch in the supply line to the motor cuts 
off the current, the motor slows down and when its 
back e. m. f. becomes weak the no-voltage release lets 
go of the lever and the spring resets the box for a new 
start. 

Electrical Connections. —In Fig. 87 is shown 
a starting box and how it is connected to the line and 
to the motor. 

The box has three binding posts marked L A and F 
or with the words Line, Armature and Field. From the 
main switch one wire goes to the L post on the start¬ 
ing box and the other wire is connected to the post 
marked L on the motor. 

The lever on the box is connected to the “line” bind- 


26 o THE BOYS' BOOK OF ELECTRICITY 


ing post. The first movement connects the line to 
the strip making the field connection. A further move¬ 
ment completes the circuit through the whole starting 
resistance to the armature. 

In the field circuit there is the magnet which is mag¬ 
netized as long as the line voltage is on the motor and 
also as long as the back e. m. f. of the motor is strong 


L/A/E 



enough to protect the motor from a dangerous flow 
of current. 

If the posts A and B were connected the no-voltage 
release magnet would be short circuited and lose its 
magnetism. As the current flows to the armature 
through the overload release magnet, should that cur¬ 
rent become too large, the magnet becomes very strong. 
Thus the iron lever C, which is pivoted at P, is pulled 




















FAMILIAR THINGS 


261 

up against the posts A and B. This kills the magne¬ 
tism of the no-voltage release and the motor is stopped 
as explained before. 

The terminals on a motor with a shunt field are 
either marked F, A and L or one can easily trace the 
connections. The post marked L is a common return 
for the armature and shunt field currents and is con¬ 
nected directly to the supply line. 

In Conclusion. —Fan motors and those used for 
sewing machines, cleaners, coffee grinders and where 
small quantities of power are needed will be found 
to be series motors with commutators. These run 
equally well on a. c. or d. c. 

The Telegraph.—Until radio grew so popular 
many boys had their own private telegraph lines be¬ 
tween their homes and those of their friends. The 
code could be learned and then there was lots of fun 
“pounding brass” back and forth. 

Radio “hams” use the International Code which 
differs slightly from Morse. Land telegraphy is a 
series of short and long silences separated by clicks 
of noise, while radio telegraphy consists of short or 
long buzzes separated by gaps of silence. 

Today a live wire boy will build a buzzer line as 
described on page 248. Then he will learn to send 
in code and to read code. Thus he will get more fun 
out of a radio receiver. 

There are plenty of telegraphs used on land wires 
today and there always will be. Radio has taught us. 
how to make a land wire carry four telephone conversa¬ 
tions and six telegraph messages at the same time, but 
it has not nor will not displace land wire telegraphy. 

The hook-up of a simple telegraph circuit is shown 
in Fig. 88. 

The Key. —The key is a switch designed for ease 
and rapidity of operation. 

The standard key moves up and down. There is a 


262 THE BOYS’ BOOK OF ELECTRICITY 


special key for high speed work, which has a sidewise 
motion. It is constructed so that when the lever is 
swung to the right the key automatically sends dots 
as long as it is held there. With this key the operator 
can send at a high speed with the least possible fatigue. 

The Sounder. —A horseshoe electromagnet is in¬ 
termittently energized by the action of the key. This 
causes a lever to strike on the metal frame and make a 
click. When the lever is released a spring brings the 


SOUNDER SOUNDER 



Fig. 88. A Telegraph Circuit. 


lever against another part of the frame with another 
click. 

The Circuit. —As shown in Fig. 88 a switch must 
be used at the “listening” end to bridge the gap caused 
by the key. Since both sounders operate when the 
man at New York sends, he may be interrupted by the 
Albany operator, who by opening his switch will cause 
both sounders to stop. 

Today the ground is not used as part of a telegraph 
circuit. The resistance of the ground is so great that 
the expense of a complete circuit of copper is justified 
by the savings in operation. 

The Telephone.—With two sets, each consisting 
of a transmitter, receiver, battery and transformer, and 












FAMILIAR THINGS 


263 


following the hook-up of Fig. 89 you could set up a 
telephone system. For a call bell you would run a 
separate pair of wires with battery, bells and push 
buttons as shown in Fig. 83. 

Before we dig into the parts of this system to see 
just how they operate, let us get a clear idea of what 
you do to the transmitter, when you speak into it. 

Sound. —Your lungs force air through the stretched 
vocal cords which vibrate so as to make the air come 
from your lips in puffs. These puffs of air follow 
each other at such close intervals that from 60 to 1,000 



of them occur in one second. Gentle as these puffs of 
air are, and rapidly as they follow each other, the 
flexible diaphragm moves each time a puff strikes it. 
The elasticity of the diaphragm, for it is a thin disk of 
elastic material, brings it back again, between the puffs 
of air. 

We must make the diaphragm of the other fellow’s 
receiver, make the same vibrations as the diaphragm of 
our transmitter. When this is accomplished, his re¬ 
ceiver will vibrate, sending into the air a series of puffs, 
which his ear translates into sound. 

The Transmitter. —You speak, as shown in Fig. 
90, into a mouth piece and through the holes in the 
guard against the diaphragm D. A screw fastens this 
to a frame holding a carbon plate C. There is a second 












264 THE BOYS’ BOOK OF ELECTRICITY 


carbon plate separated from the first by a ring of in¬ 
sulating material I. Thus a box is formed which is 
filled with carbon granules, G. 

The vibrations of the diaphragm alternately squeeze 
the carbon granules into better contact, thus lowering 



Fig. 90. A Telephone Transmitter. 


their resistance to current, and then relax the pressure 
so that the resistance becomes high. 

Looking back at Fig. 89 you will see that this voice- 
controlled resistance varies the current from the bat¬ 
tery, and that this variable d. c. flows through the pri¬ 
mary of a transformer. There is generated in the 
secondary winding of this transformer an a. c. of much 
higher pressure, which flowing along the line, affects 
the receivers. 

The Receiver. —As shown in Fig. 91, a very strong 
permanent magnet of horseshoe shape M is supported 
by a frame F. On each pole of the magnet is placed 
a coil of many turns of wire A. Size No. 28 is used 


























FAMILIAR THINGS 


265 


so as to get many turns in the small space available 
for the coils. The wires are soldered to two binding 
posts B, from which the larger telephone cord leads 
out through the hole H. Two wires are concealed in 
this cord. 

The electrical parts of the receiver are contained in 
a hard rubber casing R which fits up behind the frame 
F, and a hard rubber cap C, which when screwed down 
firmly, holds the diaphragm D and frame F, securely 



against the back casing R. The binding posts are 
insulated from, but supported by, the frame F. 

The diaphragm D is thin, flexible and of soft iron 
so as to be magnetizable. It is very close to, but not 
touching the poles of the magnet. 

We have a voice-controlled a. c. oh the line, which 
passing through the coils A, alternately reinforces and 
diminishes the strength of the magnet M. Thus the 
diaphragm M is drawn forward and released, so that 
it moves precisely as the diaphragm in the transmitter 
does. Little puffs of air are then produced by this dia¬ 
phragm, which correspond exactly to the little puffs 
that you made at your transmitter. Hence the listener 
hears sound. 


















266 THE BOYS’ BOOK OF ELECTRICITY 


The coils A are designed to make as great a change 
as possible in the magnetism of the magnet, but also 
to offer as little resistance as they possibly can to the 
current. These qualities are antagonistic, for coils of 
great magnetic strength when served with small cur¬ 



rents, must contain lots of wire, which makes high re¬ 
sistance. An ordinary telephone receiver offers about 
80 ohms resistance. 

These receivers are not used for radio reception, 
the reason for which will be explained later on. 

How the Telephone Works.—On the desk or 
table stands a telephone. The transmitter is supported 
on a stand and from the hook on the stand hangs the 
receiver. 

In a box nearby is a bell, a condenser and a trans¬ 
former. Fig. 92 shows a wiring diagram which ex¬ 
plains how this telephone outfit operates. 

The telephone stands there with the weight of the 
receiver holding the hook down, and so the two con- 















FAMIUAR THINGS 


267 


tacts at A and B are not made. The d. c. from the 
“talking battery” at the central station cannot flow 
through the bell either, for the condenser is an open 
circuit for d. c., its insulation stopping the current. 

Some one wants you. The operator connects the 
a. c. ringing dynamo to the circuit. Although your 
circuit is open at the hook switch points A and B, yet 
an a. c. current will pass its effects through a con¬ 
denser. In this way an alternating current flows 
through the condenser and bell ringing it. 

You pick up the receiver and the hook switch rises 
making contact at A and B. The d. c. now flows 
through your transmitter and primary P of the trans¬ 
former. You then talk and altering the strength of 
the d. c. current, produce an a. c. current in the sec¬ 
ondary. This current flows out on the line to the 
other fellow’s receiver. When he talks to you, the 
a. c. from his end comes through your secondary S and 
operates your receiver. 

If the parts of the telephone set were wired exactly 
as shown in Fig. 92 there would be several “troubles.” 
The bell and condenser would act as a shunt for the 
a. c. talking current, thus weakening the current sent to 
the other end of the line. Also the primary of the 
transformer would act as a shunt on the secondary. 

The telephone engineers avoid these “troubles” by 
omitting the wire from C to D and inserting a wire 
from C to E. This change in the connections also 
prevents too large a d. c. flowing through the receiver. 
For it places the bell whose resistance is 1000 ohms 
in series with the circuit that would carry d. c. to the 
receiver. This effectually blocks the 24 volt d. c. bat¬ 
tery from sending much current through the receiver. 

A desk set is shown in Fig. 93. In the cord from 
the box on the base board up to the telephone on your 
desk are three wires. Where they go and how they 
are connected is clearly shown in the picture. 


^68 THE BOYS' BOOK OF ELECTRICITY 


The Induction Coil.—In a transformer the pri¬ 
mary is served with a. c. and so the secondary fur¬ 
nishes a. c. An induction coil is a kind of transformer 



to which we serve interrupted d. c. and obtain a. c. 
To obtain a clear idea of its action try this experiment. 

Its Action. —Experiment 46.—Following the hook¬ 
up given in Fig. 94, we will connect a simple trans¬ 
former to a source of current and to a galvanoscope. 











































FAMILIAR THINGS 


269 

The secondary is to have twice as many turns as the 
primary. The core must be very soft iron, annealed 
iron wires making the best material for the core. 

Close the switch and observe the direction in which 
the galvanoscope moves. Notice that after its kick or 


a 

Fig. 94. Principle of the Induction Coil. 



momentary deflection the needle returns to a position 
which indicates that no current is flowing. Open the 
switch and note that the kick of the needle is in the 
opposite direction. 

Thus an interrupted d. c. in the primary of a trans¬ 
former will induce an a. c. in the secondary. 



You must use the astatic needles in the galvanoscope 
and you may need to use the 110 volt control panel 
with a 110 volt supply to get a large primary current. 

How It Works. —The hook-up of an induction coil 
is shown in Fig. 95. Omitting for a moment a con- 





























270 THE BOYS' BOOK OF ELECTRICITY 

sideration of the condenser, we have a primary circuit 
very much like an electric bell or buzzer. The point B 
is where the circuit is automatically made and broken. 
The soft iron armature A is attracted by the iron core 
of the coil. This breaks the circuit at B, and the pri¬ 
mary coil loses its current and its magnetic effect. Then 
the spring S moves the armature back, and contact is 
again made at B. 

The Vibrator makes and breaks the current very 
rapidly. This results in the induction of a. c. in the 
secondary, which usually having many more turns than 
the primary, produces a high voltage. 

The Condenser. —When the current is broken at 
B a spark is produced, and the current flowing through 
that spark does not stop suddenly. The quicker the 
current changes from its normal value back to zero, 
the more quickly does the magnetism disappear. Hence 
the flux cuts the secondary more rapidly. 

With a condenser connected as shown, when the 
current is broken at B, the electrons forming that cur¬ 
rent rush into the condenser, instead of making a 
spark. This makes the break a snappy one and in¬ 
creases the voltage induced in the secondary. 

Uses of the Induction Coil. —One use is to ob¬ 
tain an alternating current from a d. c. supply but 
the transformer action whereby we obtain a great step- 
up in the voltage makes the induction coil an important 
source of jump sparks. 

The very high voltage from the secondary will jump 
between the points of a spark plug and ignite explosive 
mixtures. 

Ignition.—All engines using gas, gasolene, kero¬ 
sene etc., for fuel, operate on the principle of exploding 
the compressed vapor of this fuel. 

An electric spark is used to explode the vapor. Two 
distinct types of ignition systems have been developed. 
The “make and break” often used on slow speed and 


FAMIUIAR THINGS 


271 


motor boat engines; the “jump spark” used on high 
speed engines and those whose speed must be varied 
a great amount. 

The Make and Break Spark. —The firing me¬ 
chanism is built on a plate or plug which fits into the 
side of the cylinder very near the top. As shown in 



-- 

SPR/MG 



Fig. 96. Make-and-Break Ignition. 


Fig. 96 a stationary rod holds a spring and a rotating 
shaft carries a cam. 

The electrical circuit is as shown. The kicker or 
kicking coil is a coil of wire wound on an iron core. 
When the cam makes contact with the spring a cur¬ 
rent flows. At the proper instant the cam moves away 
from the spring, and the circuit is broken. A spark 
occurs at this gap. 

The magnetism of the coil dies away and cutting the 
turns of wire in the coil induces in them a current which 
makes extra electrons move. These electrons crowding 
at the gap cause a much heavier spark than the battery 
alone could make. 

The Jump Spark. —There are several different 
types of jump spark ignition systems. Some use a 
battery, others a low voltage magneto and a few a high 
voltage magneto as the source of energy. 

In some systems the current at a low voltage is con- 


















272 THE BOYS’ BOOK OF ELECTRICITY 


nected in turn by a timer, to each of a set of induction 
coils, there being one coil for each cylinder and each 
coil serving one spark plug. 

Another method uses one induction coil and dis¬ 
tributes its output to the different spark plugs in the 
proper order. 

Ford Ignition. —A system combining a low voltage 
magneto with low tension (voltage) distribution 



avoids the need for very good insulation of moving 
parts. The essentials of this system are shown in 
Fig. 97. 

The 16 horseshoe magnets on the flywheel induce 
current in the coils fastened on the frame of the motor. 
This current flows from the magneto to the four in¬ 
duction coils. They are connected in parallel, but cur¬ 
rent flows through but one at a time. 

As the timer connects the low voltage current to 
the primary of a particular coil its vibrator acts and 
















FAMILIAR THINGS 


273 


there is induced in the secondary a high voltage which 
is delivered to the spark plug. 

A lot of wiring is saved by using the frame of the 
motor as a path for the current. The primary circuit 
is completed from the timer’s rotating contact through 
the metal of the motor back to the magneto. The 



Fig. 98. Single Coil, High Tension Distribution Ignition 
System. 


completion of the secondary circuit is obtained by con¬ 
necting the primary and secondary windings as shown 
in Fig. 97. Thus the secondary current can flow from 
the plugs through the metal of the motor to the 
rotating contact of the timer and thence through the 
primary winding. The dotted lines in the diagram 
represent paths through the metal of the motor. 

One Coil System. —From a battery as in Fig. 98, 
the current goes through the primary of an induction 
coil and then to a mechanical make and break. This 
acts as a vibrator for the coil. The cam C moves the 
spring against the contact A and allows it to snap 
away suddenly. The cam shaft is geared to make as 
many revolutions to one of the motor as there are 
cylinders in the motor. In this way the secondary 
sends out a high voltage impulse for each cylinder. 





















274 THE BOYS’ BOOK OF ELECTRICITY 

Connections from this single coil to the spark plugs 
are accomplished by a distributor. To its central con¬ 
nection D the secondary current flows. A rotating 
block E makes a firm yet easily rotated contact with D. 
The same shaft drives both C and E so they are prop¬ 
erly timed. The spring contact F almost touches the 
posts G in turn. There are as many posts as cylinders 
and each is connected to a spark plug. 

The diagram shows how both the primary and sec¬ 
ondary circuits are completed through the metal of the 
motor. 

FAMILIAR QUESTIONS 

Can you walk on a third rail without injuryf Yes. 
But you can not touch the third rail and the ground at 
the same time without experiencing a shock. For you 
would then complete a circuit. Since the third rail 
serves the same purpose as a trolley wire, you could 
hang from a trolley wire without injury as long as you 
did not also touch anything connected to the ground. 

How can birds sit on a 22000 volt trolley wire? For 
the reasons given above. There is no circuit through 
the birds, no passage of electrons and hence no ill effects. 

Can 110 volts kill you f Were this not a serious mat¬ 
ter I would make a joke and say that volts cannot kill 
you, it is the amperes that do it. The resistance of the 
skin is so high that 110 volts can not send a dangerous 
current through a strong healthy person. But a scratch 
or a sore may reduce the resistance of the skin at that 
spot. Then if we complete a 110 volt circuit, we may 
receive an injurious current, particularly a person with 
a weak heart. Make it a rule not to touch live wires. 

How many volts will it require to run my motorf 
Enough volts to push sufficient amperes through all the 
resistances of the circuit, so that the motor will run. 

It is the amperes that do the work. Amperes are 


FAMILIAR THINGS 275 

electrons in motion and they will not move unless 
pushed. 

The pushing force in a circuit is measured in volts. 
What is a 50 watt incandescent lamp? It is a lamp 
that when placed on a 110 volt circuit allows 0.45 
amperes to flow. The lamp is designed so that this cur¬ 
rent will heat the filament as hot as it is wise to heat it. 

On the 110 volt circuit for which this lamp was 
designed it takes 50 watts of power to operate it. 

You can purchase a 50-watt lamp for 120 volt cir¬ 
cuits. These lamps have a slightly higher resistance. 
On the proper circuit they use 50 watts of power. 

The candle power of a 50 watt lamp depends on 
whether it is a vacuum or a gas type and whether it 
is used on the circuit for which it was designed. 

Do abandoned steel ships move to the poles? No. 
The magnetic force of the earth is a twisting force. 
It will not pull. 



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CHAPTER XII 

„ RADIO 

Radio 

Folks Using Radio 
Sending Stations 
Sparks 
Arcs 

Alternators 
Vacuum Tubes 
[Waves 

An Interruption 

Sound Waves 

Speed 

Frequency 

Wave Length 

Wave Length Formula 

Amplitude 

Light Waves 

Invisible Light 

Electromagnetic Wave Motions 
Radio Waves 
Velocity 
Frequency 
Wave Length 
Rule for Wave Length 
Amplitude 

Production oe Radio Waves 
A Short Talk on A. C. 

Mutual Inductance 

•Coupling 

Self Induction 

Experiment 47 
Reactance 
Condensers 
Capacity 

Combined Inductance and Capacity 
Something Odd 
Distributed Capacity 
The Queerest Thing Yet 
Impedance 

Getting Radio Waves into the Ether 
Rule eor Wave Length 
An Actual Circuit 

What Carries the Radio Wave Motion to Us, 
Getting Into the Ether 
Transferring Oscillations 
What the Antenna Does 

277 


2;8 THE BOYS’ BOOK OF ELECTRICITY 


Radiating Only One Wave Length 
Listening In 
Apparatus eor Receiving 

What Does Receiver Mean 
Absorbing the Energy From the Radio Waves 
Selecting the Desired Frequency 
Interference 
Receiving Circuits 

Double Circuit Tuner 
Single Circuit Tuner 
Selectivity 
Tuning 

Entrance for 360 Only 
How Speech and Music Come 
A Carrier Wave 
Modulation 

Reception by Crystal 
A Grain of Salt 
The Vacuum Tube 
The Filament 

The A Battery 
The B Battery 
The Plate 
The Grid 

Reception of Signals 
The Detector 
An Actual Set 
Grid Condenser 
Grid Leak 
The Plate Circuit 
Non-Regenerative Receiving 
Regenerative Receiving 
Tuned Plate Circuits 
The Variometer 
The Feed Back 
The Tickler 
Amplification 

Audio Frequency Amplification 
C Battery 

Radio Frequency Amplification 
Variable Condensers 
Building Receiving Sets 
Reading Radio Hook-Ups 
Signing Off 


CHAPTER XII 


RADIO 

Radio is so named because the energy used to trans¬ 
mit signals is radiated into the air at the sender’s sta¬ 
tion. By signals I mean voice, music, interrupted or 
varied currents of electricity. 

Radio used to be called wireless. Most people do 
not realize that our supposedly new radio is the same 
old wireless of the early Marconi days in 1894. In 
1899 messages were sent across the British Channel 
and war ships were telegraphing to each other. In 
1902 messages were telegraphed across the Atlantic 
Ocean by wireless. 

The broadcasting stations are using the same 
methods for sending out waves as the amateurs are 
using, but of course with much more powerful trans¬ 
mitters. 

Folks Using Radio. —Communication between 
ships and ships and shore includes distress calls, radio 
compass work and fog signals. The transatlantic 
and transpacific ocean traffic is very heavy. Navy 
and Government business is utilizing radio to a great 
extent. The broadcasting furnishes entertainment for 
millions. The transcontinental communication by radio 
is growing. Finally 1200 boys and men talk and 
telegraph by radio every evening after 10 p. m. During 
the month of March, 1923, they sent and delivered 
160,000 messages. 

Before studying the electrical part of radio it would 
be well to take a glance at the practical side of it. A 
trip to a few sending stations would be interesting and 
279 


280 THE BOYS’ BOOK OF ELECTRICITY 


instructive. I wish you to notice the difference in the 
apparatus used to produce the same thing. 

Sending Stations. — Sparks. —Down the street is 
a boy friend of mine. He is signalling to another boy 
in a distant city. He has a Ford spark coil, a con¬ 
denser, and a place for the spark to jump across. 

He is sending short and long currents into the in¬ 
duction coil, thus sending short and long showers of 
sparks from the coil. The electricity from the sparks 
passes along his antenna and forms radio waves in the 
air. 

On any ship you will find a similar sending set 
with larger induction coils, bigger and better apparatus 
throughout, and a larger current used to send. 

Arcs. —In the sending sets of the U. S. Shipping 
Board and the Naval Stations a flame between two 
carbon rods sends out the radio waves. 

Alternators. —There are a few big stations that 
use specially designed alternators to generate radio 
waves. 

Vacuum Tubes. —Specially constructed vacuum 
tubes containing a filament, to be lighted, like an in¬ 
candescent lamp, a metal plate and a wire net work, 
are used to send out waves. 

These vacuum tubes are used by the amateurs and 
the broadcasting stations. Originally made in small 
sizes about as large as an ordinary incandescent lamp 
and giving out 5 watts, they are now made in huge 
sizes furnishing 50 kilowatts. 

Waves. —Every one of these people in each sta¬ 
tion was engaged in sending out waves. Certainly we 
must learn something about waves. 

A wave motion is a method of transferring energy 
without transferring any material. One way of 
destroying an enemy’s wooden ship would be to throw 
something violently at it. But even the ancients knew 
that concentrating the sun’s rays on a wooden ship, s 


RADIO 


281 


by means of huge bowl-shaped mirrors of polished 
metal, would furnish enough heat to set it on fire— 
provided of course the ship was in the same place 
long enough for the heat to accumulate. Heat is 
carried by a wave motion. 

If there is a chip of wood out in a pond quite out 
of my reach, I may move it up and down by throwing a 
stone, hitting it. Or I may drop a large stone into 
the water near the shore, and in this way I shall 
start a series of waves, which spreading out will travel 
to the chip and move it. 

Although the wave motion travels far, the material 
in which the wave is formed and through which the 
wave travels does not move much. 

When the wave in the water reaches the chip, it rises 
and moves forward with the wave a bit. Then as the 
wave passes on, the chip slides down the back of the 
wave to the place where it was before. It floats on 
the same old water in the same old place. The wave 
moves forward to its destination but the water stays 
where it was. 

When the wind blows across a field of grain, you 
can see a wave motion moving through the tops of the 
stems. You know that the stems are firmly rooted in 
the soil, and do not move across the field. You know 
that the tops of the stems merely vibrate to and fro, 
yet the wave does advance; you can see it do so. 

There are two kinds of waves for us to study in 
Radio Telephony, sound waves and radio waves. I 
pick out radio telephony because that is the most popu¬ 
lar branch of radio. 

Since all waves have some features alike we will take 
up sound and radio waves discussing their speed, fre¬ 
quency, wave length and amplitude. 

An Interruption^. —Some one, age 14, looking 
over my shoulder at this point, asks me: “Have you 
told them how a receiver works?” I have looked him 


282 THE BOYS' BOOK OF ELECTRICITY 


straight in the eye and replied. “No. How can I do 
that until they know what it is that the receiver is 
receiving ?” 

Sound Waves. —Anything that sets material 
vibrating at a rapid rate creates a sound wave. Now 
a sound wave is not sound. It takes three things to 
make a sound. 

1. —A body in vibration to start the sound waves. 

2. —A material to carry these waves. 

3. —An' ear and brain to change these waves to the 
sensation of sound. 

In a radio receiver the telephones or head set or 
phones, as they are variously called are the bodies that 
start air into vibration. This causes sound waves which 
the air carries to your ear and you hear. 

Speed. —The speed of sound is 1090 feet per second 
on a freezing cold day in winter, and about 1120 feet 
per second on a summer day. 

Frequency. —While listening at the phones of a 
radio receiving set this set causes the diaphragms of 
the phones to vibrate to and fro. Sometimes they 
vibrate at such a rate as would cause them to make 
200 to and fro motions in a second, provided that they 
continued to vibrate as long as that, at that rate. This 
would be a frequency of 200. At another time per¬ 
haps for one one hundredth of a second the diaphragm 
vibrated regularly and made 20 vibrations. That would 
be at the rate of 2000 in one second, or at a frequency 
of 2000. 

The frequency of the vibrations is the rate of vibra¬ 
tion. Hence frequency is the number of vibrations per 
second. 

A vibration of anything means going from end to 
end of a region and back again, including being all 
ready to do it again. Take the letters v i b r as they 
stand. If the dot over the i moved over to the r, back 
to the v and to its regular place again, it would have 


RADIO 285 

made a complete vibration. You could say that the 
dot has made an oscillation. 

Since this kind of a trip is like that which the boy 
made on page 50, which I would like you to read again, 
we may say that this dot over the i has completed a 
cycle. 

The word frequency means the same as cycle. We 
speak of a 500 cycle a. c., whose frequency is of course 
500. When referring to a body causing a sound we 
should mention its frequency. It would be correct to 
say, “A 1000 cycle sound wave,” but we do not. We 
say the equally correct thing, “Its frequency is 1000.” 

Wave Length. —When a wave motion which will 
cause you to hear sound is passing through air, it may 
be photographed. This picture shows the air to be 
compressed at some places and expanded at others. 
By expanded I mean less air than usual, and by com¬ 
pressed I mean more air than usual is at those places. 

The distance from one place of greatest compression 
over across a place where the air is stretched or ex¬ 
panded to another spot of greatest compression is called 
a wave length. 

Wave Length Formula. —When a vibrating body 
at a frequency of 500 sets up a sound wave in air, this 
wave advances at the speed of 335 meters a second. 

The first puff of air which left the body has created 
a series of compressions. At the end of one second 500 
of these compressions are distributed over a distance of 
335 meters, all evenly spaced with an equal number of 
expansions of the air in between. 

The distance a particle of air moves in completing a 
cycle is a wave length. Also the space occupied by a 
compression and an expansion of the air is a wave 
length. So dividing 335 by 500 gives 0.67 of a meter 
as the length of what is called a wave. 

This is true of all wave motions. Divide the velocity 
by the frequency and get the wave length. 


284 THE BOYS’ BOOK OF ELECTRICITY 


Amplitude. —When we bang a drum hard it gives 
out a loud sound; strike softly and the sound is not 
so loud. We say that the sound waves differed in 
amplitude. Really then amplitude means energy, for 
the more energy in the wave the greater will be the 
impression on the ear. 

There seems to be one particular rate of vibration at 
which the drum head likes to vibrate, and vibrations of 
that frequency persist and do not die out quickly. 

Why it has a natural frequency I do not know, just 
as there are many things we do not know. Nature 
decreed that it should be so. 

Hit a drum softly. The calfskin head vibrates at its 
natural frequency, sends out a sound wave of the same 
frequency and I hear a sound in my ear of that fre¬ 
quency. Yes, that sound wave had a certain wave 
length, but I really do not care about that. Since a 
frequency started it and I hear it because of the fre¬ 
quency with which my ear drum is beaten upon, let us 
stick to frequency. 

Light Waves. —Light differs from sound, yet both 
are waves. But the only resemblance between light 
waves and sound waves is in being ever expanding 
shells of disturbance. Here the resemblance stops with 
a jolt. 

To create light, electrical charges vibrate. The fre¬ 
quency of this vibration is an enormous number. The 
speed or velocity of advance is 300,000,000 meters a 
second. Light could go around the earth 7]/ 2 times a 
second. 

To get the wave length we divide 300,000,000 by 
the frequency and have the wave length in meters. 
Since the frequency is an enormous number and the 
wave length a reasonably easy number to say, when 
discussing light we talk of wave length. 

Invisible Light. —All waves of exactly the same 
character as light waves are not visible. Some have a 


RADIO 285 

frequency too high to be detected by our eyes; again, 
other waves have too low a frequency to be seen. 

Electromagnetic Wave Motions.—X-rays, visible 
light, and heat waves are all alternate electric and mag¬ 
netic energy radiated from bodies. They are formed 
by the energy thrown out from electrons as they revolve 
in atoms of materials. From electrical charges vibrat¬ 
ing in paths from a few feet to ten miles long we obtain 
radio wave motions. 

Radio Waves. —Electromagnetic wave motions pro¬ 
duced by the surging or oscillating of electrical charges 
at a frequency of from 15,000 up to 3,000,000 are those 
referred to today as radio waves. 

Velocity. —Their velocity is the same as that of 
light, being 186,000 miles a second, or, since radio 
engineers use the metric system, we will say 300,000,000 
meters a second. 

Frequency. —The frequency of the electrons as they 
oscillate in any kind of a radio frequency generator is 
the frequency of the radio wave motion. 

Wave Length. —It is rather unfortunate that we 
got in the way of talking about 200 meter, 360 and 400 
meter waves, meaning that their wave lengths were 200, 
360 and 400 meters. Unfortunate, because it is the 
frequency of the vibration or the frequency of the 
oscillation of the electricity at the generating station 
that puts the broadcasting into the air as a wave of 
certain length. 

Your radio receiving set will absorb energy well or 
badly, according to the frequency of the energy that 
passes your home. When you have it adjusted cor¬ 
rectly only one group of frequencies will be absorbed 
and the others rejected. So we should talk about radio 
in terms of frequency. 

We all fell into the habit of talking about a. c. house 
and factory supply as 60 cycle a. c. We talked about 
the frequency of audible sound as being for musical 


286 THE BOYS' BOOK OF ELECTRICITY 


sounds from 16 to 3000 and for speech from 200 to 
2000. True, we usually say a pitch of 200 to 2000, 
but pitch is but another word for frequency. 

But when we came to radio we were too lazy to say 
a frequency of 833,000 or 750,000, and said instead 
360 or 400 meters. 

Rule for Wave Length. —Divide 300,000,000 by 
the frequency to obtain the wave length in meters. 

If you know the wave length, divide it into 300,000,- 
000 to find the frequency. 

Amplitude. —Nearly every picture that the word 
amplitude brings before the mind will give a wrong 
impression when applied to a radio wave motion. Like 
many technical words handed down to us, it has a def¬ 
inite meaning quite different from that conveyed by 
the sound of the word. Amplitude means Energy. 

Imagine a real dyed-in-the-wool scientist taking a 
little recreation in the breakers at the seashore. They 
are cute little ones about four feet high and roll in reg¬ 
ularly as a clock, every three seconds. 

“Constant frequency of ^ 3 ,” says the scientist, as 
he turns his back and enjoys the regular slap, slap of 
the breakers on his back. “Constant amplitude, also," 
says he, as they each hit him with a regular and equal 
force. 

Then suddenly, Bing! He receives a wallop from an 
eight-footer. Over he goes. On struggling to his feet, 
precisely three seconds after the bing, comes another 
wave, eight feet high. Bang! Over he goes again. Up 
he comes, and in two seconds is braced for the next 
wave. On they come, three seconds apart but eight 
feet high. 

“Well," says our scientist, “the frequency of these 
waves is the same, but their amplitude has greatly in¬ 
creased." 

Remember that amplitude means energy. 


RADIO 


287 


Production of Radio Waves. —First we want 
electrons to surge to and fro, or oscillate, as we usually 
say. A spark coil, a specially designed high frequency 
alternating current generator, an arc lamp with the flame 
between the carbons at proper adjustment or a “vacuum 
tube” will all start electrons oscillating. 

We now wish to encourage those electrons that are 
oscillating at a definite frequency to continue at that 
frequency. We also wish to discourage and perhaps 
entirely prevent electrons from oscillating at any dif¬ 
ferent frequencies. 

We must also cause the electrons to set up an electro¬ 
magnetic wave motion. 

There is so much here that needs explaining that I 
will start with a little talk on a. c. and then take up the 
points in the production of a radio wave motion one at 
a time. 

A SHORT TALK ON A. C. 

Mutual Inductance. —In describing the induction 
coil and the transformer it was stated that the magnet¬ 
ism of the primary coil transferred energy into the sec¬ 
ondary. The name of this process is induction, or in a 
more explaining way, electromagnetic induction. 

The current which was generated in the secondary 
coil produced a magnetic field, which of course must 
transfer energy into any coil near it. The primary coil 
is very near. So the secondary acts back on or reacts, 
as we call it, on the primary. This process of mutual 
action and reaction is called mutual inductance. 

Any coils in any electrical apparatus near each other 
will have a mutual inductive effect on each other. Plac¬ 
ing these coils with their axes at right angles to each 
other reduces the mutual inductance to zero or almost 
zero. 

In radio work the amount of mutual inductance be¬ 
tween two coils is called the coupling. 


288 THE BOYS’ BOOK OF ELECTRICITY 


Coupling. —Loose coupling is obtained when the 
coils are far apart or at an angle to each other. Tight 
coupling is obtained by placing axes of coils parallel or 
nearly so, and near each other. 

When one coil is within the other, axes being parallel 
or nearly so, we have very tight coupling. 

Self Induction. —Experiment 47.—Connect 6 dry 
cells in an arrangement of 3 in series and two rows in 
parallel. Solder one wire from this battery to the han¬ 
dle end of a coarse cut file. Holding the other wire 
from the battery in your hand, draw it along the rough 
surface of the file. Do this quickly and then take wire 
from the file, else the short circuiting will injure the 
battery. 

You will not see any sparking at the breaks of the 
current caused by the rough teeth of the file. 

Insert in the wire you had in your hand any con¬ 
venient electromagnet, a bell, primary of an induction 
coil, with vibrator screwed up firmly. When you draw 
the wire across the file you now get a series of sparks. 

These sparks are caused by the electromagnetic in¬ 
duction of the magnetic field of this coil on itself. This 
action is called self induction, or more briefly, induc¬ 
tance. 

All electrical apparatus containing coils will show this 
effect of inductance. Since every wire carrying current 
has a magnetic field around it, even straight wires show 
some inductance. 

Radio sets contain coils, thus causing, by mutual in¬ 
duction, energy to be transferred between them; some¬ 
times to places where we do not want it. We then turn 
these coils at right angles to each other to kill the induc¬ 
tive effect. 

Reactance. —Inductance causes coils to offer more 
opposition to a. c. than it would to d. c., because the 


RADIO 


289 


a. c. is compelled to build up a magnetic field twice as 
often each second as the number expressing its fre¬ 
quency. This extra work that d. c. does not do reduces 
the amount of current which the a. c. e. m. f. can force 
through the inductive circuit. 

This extra resistance to a. c. we call reactance. 

To calculate the reactance of an inductive circuit 
multiply the frequency of the a. c. in it by the henrys 
of inductance of the circuit and then by 6.3; the answer 
will be in ohms. 

Condensers. —When there is only a condenser in a 
circuit it is electrically combined with the resistance of 
the wires leading to and from it. This condenser offers 
opposition to the oscillations of the electrons. This we 
call capacity reactance. 

The capacity reactance of a condenser is calculated 
by multiplying the frequency of the a. c. in the circuit 
by the capacity in farads and then by 6.3, this answer 
to be divided into 1. The final answer is the capacity 
reactance in ohms. 

Capacity. —A condenser in a circuit offers a place 
for electrons to accumulate. If a coil was choking back 
a. c. and a condenser were placed in the circuit, then 
the condenser would afford a waiting room for the 
electrons that could not get through the coil. 

Combined Inductance and Capacity. —Please 
read the last paragraph again and then imagine a cir¬ 
cuit with a coil of 15,600 microhenrys inductance in 
series with a condenser of 100 microfarads capacity 
and a. c. supplied to this circuit at a frequency of 127. 

The coil says to the a. c. e. m. f., "Wait. You must 
devote part of your pressure to forcing my magnetic 
field into space.” The condenser says, "Come on, you 
electrons, there is lots of room here.” 

The result is interesting. While the coil is acting as 
a dam to the electrons at one point in this series circuit, 
which would result in small flow of electrons from the 


290 THE BOYS' BOOK OF ELECTRICITY 


a. c. supply, the condenser is acting as a waiting room 
for those electrons that can not go through the coil. 
Hence the same number of electrons flow from the 
supply as if the coil and condenser were not there. 

We see, then, that in a series circuit the inductance 
and papacity may be made to balance each other, and 
the same a. c. will flow as if the condenser and coil were 
not there. 

Something Odd. —Suppose you had an a. c. supply 
circuit and that you attached to it, just as you would a 
lamp which is in parallel, a coil whose inductance is 
10420 microhenrys. To this same circuit attach a con¬ 
denser of 150 microfarads capacity. The coil and con¬ 
denser will be connected in parallel on the same circuit. 

After a fraction of a second the coil and condenser 
become charged and then the fun begins. The a. c. 
reverses its direction. The coil says to the onrushing 
electrons “Wait." Seeing a convenient waiting room, 
the condenser, they rush in there. Just at the moment 
when the poil is ready to conduct electrons, the con¬ 
denser is getting uncomfortably full and the electrons 
rush out and dash through the coil. 

In this way there is a continual flow of electrons 
forming an a. c. through coil and condenser and yet 
not a single electron is sent out from the supply. The 
generator in the power house supplies a. e. m. f. but no 
movement of electrons. If the generator pressure is 
100 volts, and frequency 127, there are 12 amperes 
flowing through coil and condenser and no extra 
amperes flowing through the supply circuit from the 
generator. 

These queer things about a. c., coils and condensers 
are utilized in transmitting and receiving radio signals. 

Distributed Capacity. —All wires running close 
to each other and parallel form small condensers. All 
coils have a condenser effect between the wires of their 
windings. It is true that certain coils are wound in a 


RADIO 


291 


special manner to reduce this capacity, yet some is there. 
These capacities are called the distributed capacities, as 
contrasted to the concentrated capacity of a condenser. 

When figuring what a circuit will do, do not forget 
the distributed capacity. 

The Queerest Thing Yet. —The capacity of a 
condenser depends on the frequency of the a. c. that 
charges it. The change is not great, but sufficient to be 
of great importance in the transmission and reception 
of radio signals 

Impedance. —The total opposition of a circuit to 
a. c. is called the impedance. It is composed of the 
resistance, the inductive reactance and capacity reactance 
all combined. 

The impedance of any circuit may be very low if 
the inductive and capacity reactances cancel each other. 

Since the capacity of a condenser changes with the 
frequency it is possible to have a coil and a condenser 
whose reactances cancel at only one frequency. 

Such a circuit would have a high impedance at all 
but a few frequencies. At these few the impedance of 
the circuit would be low, and at one of these frequencies 
the impedance would be very, very low. 

This effect of very low impedance at one frequency 
is of great importance in the sending and reception of 
radio signals. 

Getting Radio Waves Into the Ether. —There 
are several things to do. 1. We must make electrons 
oscillate at high frequency. 2. Compel them to oscillate 
at a definite frequency. 3. Let them form electromag¬ 
netic waves. 

1. The most economical source of oscillating elec¬ 
trons is an alternating current of radio frequency from 
an a. c. dynamo. 

On account of the large bulk and weight of these 
dynamos, when moderate power is sufficient vacuum 
tubes are used to generate the a. c. of radio frequency. 


292 THE BOYS' BOOK OF ELECTRICITY 

The power for the trans-oceanic traffic is furnished by 
a. c. dynamos and the power for the broadcasting comes 
from vacuum tubes. 

2. To compel the electrons to oscillate at a definite 
frequency we need a circuit of certain electrical char¬ 
acter. 

Let us first agree exactly upon what we want to do. 
Suppose that I have a license from the Government of 
the United States to transmit on a 400 meter wave. 
What really does that mean? That I am permitted to 
radiate into the ether electromagnetic waves caused by 
electrons surging to and fro (or oscillating) at a fre¬ 
quency of 750,000 (or making 750,000 oscillations per 
second). 

Suppose then I arrange a circuit of the proper elec¬ 
trical length so that it takes 1/750000 of a second for 
an electron to make a complete trip through and back. 
Then I will have an oscillation circuit with a natural 
period of 1/750000 of a second, and the frequency of 
the oscillating electrons surging in it will be 750,000. 

When you think it over it seems as if the time occu¬ 
pied in going through the oscillation circuit were the 
important thing. It is. How would it be, then, instead 
of making the oscillation circuit so long and hence 
bulky, to arrange to have the electrons delayed. A 
clever arrangement of coils will not only put a long 
electrical circuit into a small space but the inductance 
of the coil will delay the electrons. Condensers may 
also be used, furnishing places for the electrons to hide 
in for fractions of seconds, thus delaying them. 

Rule for Wave Length.—Radio engineers have 
found that 1885 multiplied by the square root of the 
product of the capacity in microfarads and the induc¬ 
tance in microhenrys will give the wave length radiated 
by an oscillation circuit. The wave length divided into 
300,000,000 will give the frequency of the oscillating 
electrons. 


RADIO 


293 


An Actual Circuit. —An oscillation circuit will 
have the general form of Fig. 99A. The source of 
radio frequency alternating current (r. f. a. c.) fur¬ 




nishes oscillating electrons and the adjustable inductance 
L and the variable condenser C may be made to furnish 
just the proper amount of delay, so that an electron 
needs 1/750000 of a second to oscillate from P to F 
and back again. 

























294 THE BOYS’ BOOK OF ELECTRICITY 


What Carries the Radio Wave Motion to Us?— 

It seems that no material is needed. The radio waves 
pass through air, brick and stone yet do not use these 
materials to travel on. Radio waves go through a 
vacuum. 

Since we do not know what the radio waves travel 
on and yet feel that they must have something to be in 
and travel on, we use the word ether, to express an 
imaginary substance. 

The ether , then, is in a vacuum and in everything, 
and on this ether the radio waves travel. 

Getting Into the Ether. —We now wish to form 
radio waves in the ether. The closed oscillation circuit 
of Fig. 99A will not radiate energy well. An open 
oscillation circuit is what we need. In Fig. 99B an 
open oscillation circuit is shown. It is composed of 
the antenna A, an inductance O, a condenser C. A. 
and a ground connection. 

With the adjustment of the inductance O and of the 
condenser C. A. we may make the time constant of the 
circuit 1/750000 of a second. 

As the electrons oscillate in the closed circuit by the 
mutual inductance between the coils L and O energy is 
transferred from the closed circuit to the open circuit. 
The combination of the coils O and L is called an 
oscillation transformer. The tighter the coupling be¬ 
tween these coils the more energy will be transferred. 

But it is not merely energy that we want, it is the 
transfer of energy at one particular frequency and not 
at any other. 

Transferring Oscillations. —To explain why an 
electron in L oscillating at a frequency of 750,000 will 
cause an electron in O to oscillate at the same frequency 
I must use a simpler diagram. 

Since the coil L is merely a long wire coiled into a 
small space, let us unwind it and stretch it out straight, 
as in Fig. 100A. Let us do the same with the coil O. 


RADIO 


295 


Remembering that electrons dislike and repel each 
other, let us start to find out how the frequency in L 
is transferred to O. 

In any copper wire (or any material, in fact) there 
are a few electrons wandering around in an aimless 


CA 

EARTH » I 


o 




<zzz 


CA 


IU 

7rrm/rr>r»r?rY \—, 

EARTH 'I I * 


B 




-w 


Trrrr. 

EARTH 


1 V& 

TH ^ I 


9 ...• • » » f , 

~ <»- • • • > * 


Fig. 100. Transferring Oscillation. 


haphazard fashion. When an electron from the r. f. 
a. c. generator arrives at the point a on the wire L it 
will repel any wandering electrons at b on the wire O 
which are moving towards c. As the electron at a 
moves along L to c it drives the electron on O which 
was at b ahead of it. This crowds all movable electrons 
in O up into the antenna A. 

The situation is now as shown in Fig. 100C; a lot 

























596 THE BOYS’ BOOK OF ELECTRICITY 


of electrons are on L and they have repelled an equal 
number of the electrons from O into the antenna A. 
The 1/750000 of a second has now passed and the r. f. 
a. c. generator reverses its e. m. f. and calls the elec¬ 
trons on T back. (Or pushes them back.) 

So many electrons are crowded on the antenna A 
that there is a pressure tending to push them out again. 
As the electrons on T retreat from c through the point 
a, the electrons come rushing out of the antenna, and 
finding those in T “on the run,” those in O actually 
help to push those on T along back to the generator. 

In 1/750000 of a second the r. f. a. c. generator re¬ 
verses and the whole cycle of events occurs over again. 

Thus the oscillating electrons in the closed circuit of 
Fig. 99B create an oscillation of electrons in the open 
circuit at the same frequency. 

The same thing will happen in precisely the same way 
even if O and L are the same wire. The energy of the 
r. f. a. c. may be applied directly to the open circuit 
and the oscillations of electrons will take place as de¬ 
scribed. Such a combination of the circuits is shown 
in Fig. 101. 

Please notice that the antenna and ground make a 
huge condenser. Fig. 99 makes this clear. Notice that 
this condenser may be charged and discharged at the 
frequency of 750,000. Fig. 100 and the discussion of 
that illustration shows how this may be done. 

What the Antenna Does. —The antenna, which 
for transmitting is a group of wires parallel to each 
other, hung high up in the air and insulated from every¬ 
thing but the transmitter, forms one plate of a con¬ 
denser. The earth is a conductor and is connected to 
the transmitter. The air between the antenna and the 
earth forms the dielectric of the condenser. 

The r. f. a. c. generator through the oscillation cir¬ 
cuits charges this condenser at a frequency of 750,000. 
This condenser can not discharge through such a thick 


RADIO 


297 


layer of air as there is between the antenna and ground. 
Nor can this condenser discharge through the trans¬ 
mitting set which is connected to the antenna and to 
the ground, because the set is pushing out energy with 
such force. You can’t pour a pitcher of water into a 
hose from which water is flowing with some force. 
Hence the charge leaks off the antenna at a frequency 



Tr rs/r>/ - / - s 7- rr 7? 

EARTH 


Fig. 101. Single Circuit Transmitter. 

of 750,000, in much the same way as electrostatic 
charges leak from the lightning rods of a building. 

This leakage from the antenna-earth condenser sets 
up what we call an electro-magnetic wave motion which 
has a frequency of 750,000 and a wave length of 400 
meters. 

For a wave length of 360, read the last six pages 
again, using 833,000 for the frequency, 1/833000 of a 
second for the time constant of the circuit and 360 for 
the wave length. 

These waves carry the energy which is received, and 
as this energy is spreading out as the waves advance, 
the further away you are from the transmitting station 
the less energy you receive. 

Radiating Only One Wave Length.— Only one 
wave length should be put into the ether. In this trans¬ 
mitter which I have been describing the method of tun- 









ag 8 THE BOYS’ BOOK OF ELECTRICITY 

ing the circuits for oscillations of a frequency of 750,- 
000 has been explained. A certain combination of in¬ 
ductance and capacity will do this. This combination 
effects two things. First, the character of the circuit 
compels electrons to take 1/750000 of a second to oscil¬ 
late. Secondly, the impedance for the frequency of 
750,000 is so low that very little energy produces a 
large flow of electrons. 

Any electrons oscillating at any other frequency will 
find the impedance so great that their energy will be 
used up very quickly. 

In the circuits as we have tuned them for a fre¬ 
quency of 750,000 only these oscillations will persist. 
All other frequencies will die out, due to high im¬ 
pedance. As we say in technical slang, “They are 
damped out. ,, 

Listening In.—We will now proceed to absorb 
the energy of the radio wave motion. Then translate 
the alternating current which is at radio frequency to 
a direct current interrupted at audible frequency. 
The telephone receiver will then respond to the d. c. 
interrupted at audible frequency and we will be 
listening in. 

The various steps in the process are: Absorption of 
the energy from the electromagnetic waves. Permit 
only those of one frequency to set up oscillations. 
Transform these r. f. oscillations which are a. c. into a 
varying d. c. of audio frequency. Then the phones do 
the rest. 

Apparatus for Receiving.— 1 . The absorber, 
which is the condenser formed by the antenna and the 
ground. 2. The selector of the desired frequency, 
which is the tuner. 3. A rectifier or changer of r. f. 
a. c. to r. f. d. c., which is called by every one a de¬ 
tector, although it does not detect; it rectifies. This 
may be a crystal or a vacuum tube. 4. A device to 
change electrical impulses of d. c. into sound, which is 


RADIO 


299 


the phones. Fig. 102 gives several hook-ups of receiv¬ 
ing circuits. 

What Does Receiver Mean? —The combination 
of a tuner and a rectifier is called by the general public 
a “receiver.” A receiving set is a better name. To your 
radio receiver you attach telephone receivers. This 
makes confusion. To avoid this we will call a com¬ 
bination of a tuner, a rectifier and telephone receivers 
by the name of a receiving set, and the telephones we 
will call phones. 

A pair of phones with a band to hold them on the 
ears is frequently called a head set. 

A single phone, usually of special construction, at¬ 
tached to a horn to reinforce the sound, is called a loud 
speaker. 

Absorbing the Energy From the Radio Waves.— 

Erect an antenna as high as possible from the ground. 
For reception, a single wire is almost as good as several. 
Attach your receiving set to the ground and to the 
antenna. 

The condenser formed by the antenna and ground 
is charged by the radio waves passing it. It can dis¬ 
charge through your open oscillation circuit and in 
doing so would set up oscillations at many frequencies 
were it not that you have adjusted the inductance and 
capacity of the circuit to encourage by low impedance 
a particular frequency and to damp out by high im¬ 
pedance to them only, all other frequencies. 

Selecting the Desired Frequency. —Since the 
antenna is probably 100 feet long and the “lead in” 
from the antenna to the receiving set may add another 
50 feet of wire, your adjustable inductance and ca¬ 
pacity will have a hard job of exactly tuning the open 
oscillation circuit. It is hard for a small dog to wag 
a large tail. 

But you may time the closed oscillation circuit of 
Fig. 102A very accurately, or “sharply,” as we say, 


3oo THE BOYS’ BOOK OF ELECTRICITY 

for here the inductance L and the condenser C contain 
a large proportion of the impedance of the circuit. Here 
a large dog wags a small tail. 

The real selector of the desired frequency is the 
closed oscillation circuit, which enables the receiving 
set to be tuned sharply. A tuner that can be tuned 
accurately is said to be sharp. A very sharp tuner is 
said to be critical. Such a tuner must be tuned exactly, 
else the signals are very weak. 

Interference. —Poorly designed tuners will not 
prevent you from hearing several signals at the same 
time. This is called interference. The process of re¬ 
moving interference by adjustments of the tuning cir¬ 
cuits is called “tuning out interference.” 

Receiving Circuits. —There are three distinct 
parts to each receiving set, the tuner, the changer of 
a. c. to d. c., and the phones. 

When we talk of this and that kind of a circuit we 
are referring to the arrangement of the parts of the 
tuner and to the devices that are assembled to make 
the tuner. 

Double-Circuit Tuner. —In Fig. 102A we have 
an open oscillation circuit consisting of the condenser 
formed by the antenna and the earth, together with a 
connection between the antenna and earth. This con¬ 
nection consists of an inductance O and a condenser 
C. A., both of which are variable so that we may tune 
the open oscillation circuit. 

Coupled to the inductance O is an inductance L. 
This combination may be made in different ways and 
may be known as a loose-coupler, a vario-coupler, or 
coils with fixed coupling. The names are taken from 
the mechanical arrangement of the coils and are fairly 
indicative of their arrangement. 

The inductance L is variable and is shunted by the 
condenser C. Thus the closed oscillation circuit may 
be tuned. 


RADIO 


301 


Since we have two oscillation circuits this tuner is 
called a Two-circuit or a Double-circuit Tuner. 

When the crystal was displaced by a vacuum tube, 
extra circuits were added but the old name stuck. 




A 



Single-Circuit Tuners. —This name is not a cor¬ 
rect one because all tuners have two circuits, the open 
and the closed oscillation circuits. Perhaps the single 
inductance suggested the name. While incorrect, this 
name will in all probability persist. The circuit is shown 
in Fig. 102B. 


























302 THE BOYS’ BOOK OF ELECTRICITY 


Selectivity. —The Two-circuit tuner of Fig. 102A 
will tune sharper than a Single-circuit tuner like Fig. 
102B. 

The Two-circuit tuner has greater power of select¬ 
ing the desired wave length but is apt to furnish weaker 
signals. 

The Single-circuit tuner has less selectivity but gives 
louder signals. 

Tuning. —The process of making a receiving cir¬ 
cuit an electrical twin to the sending circuit is called 
tuning. These circuits may not look alike, they may 
not have the same kind of apparatus, but if the product 
of the microfarads of capacity and the microhenrys of 
inductance of the two circuits are equal, then considered 
as oscillation circuits they are identical. In two such 
circuits electrons put in motion will surge to and fro 
at the same frequency in each. 

Perhaps the electrical explanations of why we can 
permit a wave length of 360 to enter a tuner and yet 
block off waves of 400 and 300 has not made you 
understand this process. If you will study the explana¬ 
tion you will understand it, but there is a way to help 
you to an understanding, and here it is: 

Entrance for 360 Only. —In Fig. 103 there is 
shown a snake trap. The entrance E is wide and in¬ 
viting. There is a runway leading to the reception 
room. This trap is designed to catch one kind of snake 
only, the kind called by scientists 360. It is so ar¬ 
ranged as to prevent other kinds from getting into 
the reception room. 

The runway is made by two walls, just far enough 
apart that a 360 snake can make his wiggles as he 
makes his sinuous way into the runway. 

Along the center line of the runway are a number 
of posts, and they are evenly spaced just as far apart 
as the runway is wide. 

Along comes Mr. 360 Snake. Smelling an attractive 


RADIO 


303 


meal in the reception room he wiggles in the entrance 
and along the runway with perfect ease. 

The width of the runway is wide enough for his 
graceful curves to be made in. The posts are just the 
right distance apart for the shape of his wiggles so 
that as in Fig. 103, he moves along without hindrance. 

But when Mr. 400 Snake comes along, with his par¬ 
ticular and unalterable shape and size of wiggle, he 



has trouble. The runway is too narrow for his sinuosi¬ 
ties. His body is uncomfortably bent and soon he 
slams his head against a post. If he could change his 
shape of wiggling he could get through but he is a 
400 shaped snake and so he scrapes his sides and runs 
into posts until exhausted he quits. 

Now saucy little Mr. 300 Snake comes along with 
his snappy little wiggles. The walls do not bother him, 
there's lots of room. Merrily he slithers along when 
bang goes his head into a post. Soon he quits. Those 
posts have been adjusted with a cleverness that is too 
much for any snake but a 360 kind. 

This selective snake trap may not be placed on the 
market but it seems that it should work. 

In radio reception the clever arrangement of in¬ 
ductance and capacity does keep out undesired fre¬ 
quencies. 












304 THE BOYS’ BOOK OF ELECTRICITY 


Now we know how to absorb that frequency or as 
you would say that wave length which we desire, sup¬ 
pose we see what we are absorbing and by tuning 
transferring that and only that over to the rectifier. 

How Speech and Music Come.—A Carrier 
Wave. —The transmitting station generates a carrier 
wave of a certain frequency, say 833,000 cycles per sec¬ 
ond. When they are ready to “send,” their r. f. a. c. 
generator, which usually is a vacuum tube, is started 
and a carrier wave is placed in the ether. To help our 
minds understand we draw a picture. This picture in 
Fig. 104 is not a picture of the wave. It merely is a 
diagram that helps our minds to grasp the method of 
transmitting speech or music. 

At C we represent the carrier wave of frequency 
833,000, which takes 1/833000 of a second to make a 
cycle of values of current. As long as the station is 
transmitting or “on the air” as we say, this carrier 
wave is sent with absolutely regular frequency and 
equal amplitude. Equal amplitude would be expressed 
better by saying, “and constant energy.” The distance 
marked C in the diagram represents 4 amperes of a. c. 
Hence the distance C represents the energy of the 
carrier wave. 

The band plays into a telephone transmitter. Ex¬ 
actly as in the telephone in your home the current in 
the transmitter is changed by the transformer to an 
audio frequency a. c., with a frequency of any where 
from 200 to 3,000. 

Modulation. —By a device called a modulator this 
audio frequency is made to alternately add and sub¬ 
tract energy from the carrier wave. We say that the 
amplitude (energy) of the carrier wave is changed 
and it has become a modulated (changed) carrier wave, 
as at B in Fig. 104. 

Suppose the tune played by the band at a certain 
time has a frequency of 500. Then for periods of 


RADIO 


305 


1/500 of a second the carrier wave will undergo a 
series of changes in amplitude. 

Let Fig. 104 help you to understand that the carrier 
wave goes on steadily at a frequency of 833,000, but 
that its amount of energy (amplitude) is varied at a 
frequency of 500. 

This modulated carrier wave of radio frequency has 
its energy changed at an audio frequency. 

Getting this last paragraph firmly in your head and 
a study of Fig. 104, not as a picture of a wave, for it 



Fig. 104 . A Modulated Carrier Wave. 

is not that, but as a diagram to help you to understand, 
ought to make you understand how the speech and 
music come to us. 

Reception by a Crystal. —In the first part of the 
book there was a discussion of materials and their in¬ 
ternal structure. A mineral crystal such as galena is 
composed of electrons. When the energy of the oscil¬ 
lating electrons in the oscillation circuit arrives at the 
crystal, an alternate push and pull is exerted to set the 
electrons of the crystal in motion. 

Such a crystal resists the push and pull unequally, 
so that there is a greater movement of the electrons in 
one direction than in the other. This action is more 
unequal at certain places. We then attach one circuit 
to the place of greatest inequality of action. 

























/.R.F.D.C. MOOULATED AT A. F. 


306 THE BOYS’ BOOK OF ELECTRICITY 



Fig. 105 . Action of a Crystal. 






















RADIO 


307 


Then the crystal rectifies. It changes the r. f. a. c. 
into an interrupted r. f. d. c. Since the r. f. a. c. was 
modulated (had its energy varied) at an audio fre¬ 
quency, the i. r. f. d. c. which passes through the crystal 
is also modulated at audio frequency. 

The changes of the energy of the d. c. at a frequency 
of, say, 500 will cause the phones to emit a sound of 
that frequency, each group of energy acting as a short 
current of d. c. 

But the crystal also allowed some r. f. a. c. to pass. 
The small condenser B. C. in Fig. 102, called a by-pass 
condenser, permits this to flow around the phones. 

In Fig. 105 I have pictured in a diagram what hap¬ 
pens when a crystal enables you to hear the sounds that 
originally varied the amplitude of the wave. In 106 
I have given an illustration which will help you to under¬ 
stand the rectifying action of the crystal. 

A series of narrow waves are moving in towards a 
breakwater C. Some source of energy out at A causes 
these waves to be higher and lower in groups, but does 
not alter the frequency of their arrival at C. The break¬ 
water was built too low to stop the waves, but it does 
cut off the lower part of the wave motion and permits 
only the tops to pass. The crystal acts like this break¬ 
water. 

When these waves strike against a boat each little 
narrow wave will not rock the boat, but each group of 
waves will move it. Thus the motion of the boat is as 
if a wave motion like the black line of Fig. 106 came 
against it. The diaphragms of the phones act like the 
boat. 

A Grain of Salt. —All illustrations from everyday 
life or from things easily within our ability to under¬ 
stand, which are intended to make clearer ideas that 
are rather difficult to understand, must not be taken too 
literally. Nor must they be taken as meaning that the 
electrical thing acts exactly like the snake trap or the 


308 THE BOYS’ BOOK OF ELECTRICITY 

water waves. Use the illustrations to get your mind 
running along the proper line of thought and then try 
to master the electrical principle from the electrical ex¬ 
planation of it. 

The Vacuum Tube.—This is a device that does 
not pass the received energy to the phones, as a crystal 
does, but instead uses this energy to open and close a 
valve, which controls a more powerful source of energy. 



A 

Fig. 106 . Explaining the 

For this reason vacuum tubes are often referred to as 
valves. 

Thus the energy operating the phones may be many 
times greater than that absorbed by the antenna. 

The vacuum tube is a glass bulb from which the air 
has been pumped out. Tubes in which the vacuum is 
almost perfect are called high vacuum or hard tubes. ; 
A tube in which a little gas has been inserted, after the 
air was all pumped out, is called a soft tube. The soft 
tube is more sensitive as a detector than a hard tube. 

In the vacuum is a heated filament, a cold plate and 
a wire fence or gridiron of wire. They are called the 
filament, the plate and the grid. 

The Filament. —An inspection of Fig. 107 will 
show an incomplete circuit starting from P through 



















RADIO 


309 


the B battery, the phones and the filament F. The gap 
from F to P is in a vacuum. To bridge this gap and 
send electrons through the phones we might cause the 
filament to send out a stream of electrons with some 
force and arrange that the plate exert a strong pull on 
these electrons. This is exactly what we do. 

The A battery heats the filament, for to get electrons 
out of any material we must make it very hot. When 



Action of a Crystal. 


fairly hot, atoms are boiled out of any metal and, like 
boiling water, it evaporates or boils away. When at a 
higher temperature electrons are boiled out also. 

The hard dense metal tungsten is best suited to fur¬ 
nish a hot filament from which we can boil out a lot of 
electrons and yet be certain that as long as the filament 
is in a high vacuum it will last about 1000 hours before 
enough atoms are boiled off to destroy the filament. 

A thin, narrow platinum ribbon covered with a thin 
coating of oxides requires a lower temperature and less 
power to boil out electrons. 

To prevent these filaments from burning up they are,; - 
as I told you, sealed up in a vacuum. In the same 
vacuum tube with the filament is a cold metal plate to 
catch the electrons boiled out of the hot filament. 














3io THE BOYS' BOOK OF ELECTRICITY 


Electrons flow from a place of negative potential over 
to one of positive potential, hence if the hot filament is 
charged negatively then the high temperature boils elec¬ 
trons off and the negative condition urges them away. 

The A Battery is not a part of the oscillation circuit. 
It is a battery of the proper voltage and ampere-hour 
capacity to heat the filament. It is connected to the 



circuit so as to give the filament a negative charge. A 
storage battery or dry cells are used according to the 
type of vacuum tube used. A rheostat is used to con¬ 
trol the amount of current in the filament. 

The B Battery is usually composed of dry cells. It 
furnishes from 16 to 45 volts pressure. Its purpose is 
to give the plate a strong positive charge and cause it 
to pull over to the plate all the electrons that the filament 
can boil off. 

Following the circuit in Fig. 107 from the negative 
terminal around to the filament you will perceive that, 
while the + end of the B battery makes the plate at¬ 
tract electrons, the — end of the battery is sending a 
stream of electrons to the filament for it to boil off. 

* Now you see how a stream of electrons may flow 
; from F to P, through the phones back to F. And 
L notice that this is a one direction flow and so is d. c. 









RADIO 


31 1 

The Plate. —This cold plate of molybdenum is 
made large enough so that the electrons emitted by the 
filament will be sure to land on the plate. Its work has 
been described in the preceding paragraph. 

T he Grid. —This is a device that will make the elec¬ 
trons stop and start. It consists of a network of wires 
and is placed between the filament F and the plate P. 

The grid is nearer the filament than the plate is and 
so exerts a greater influence on it. If a switch K en¬ 
ables first the positive and then the negative end of the 
battery D to be connected to the grid G, then this is 
what happens. 

When the grid is positive it exerts a strong pull on 
the electrons from the filament F. As they rush towards 
the grid, which you remember is a network of wires, 
very few hit the grid but pass through its meshes and 
feeling the pull of the plate go on to it. 

But when the grid is made negative it says to the 
electrons boiling off of the filament, “Stop. Go back.” 
Because the grid is nearer the filament than the plate is, 
the repulsion of the grid may be weaker than the pull 
of the plate, and yet its action predominates and so it 
can stop the electrons. 

Thus the grid determines whether the electrons may 
rush from F to P or not. When they are permitted 
to flow the B battery furnishes the power to make them 
move. 

Reception of Signals.—Signals meaning voice, 
music, telegraphy or any kind of modulation (change 
of energy) of the carrier wave. 

Suppose the grid G of Fig. 107 to be connected to 
the antenna circuit or coupled to it by an oscillation 
transformer. In either case there will be set up in the 
wire leading to the grid oscillations of electrons at radio 
frequency. 

Consider the electron e. The first part of an oscilla¬ 
tion in that wire sends the electron into the grid. The 


312 THE BOYS’ BOOK OF ELECTRICITY 


grid becomes negative and says, “Stop,” to the electron 
trying to go from F to P. Then there is no current in 
the phones. The second part of the oscillation pulls 
the electrons out of the grid. The grid becomes posi¬ 
tive and says, “Come,” to the electrons trying to go 
from F to P. Then there is current in the phones. 

There are, of course, intermediate actions according 
to the amount of energy in the modulated carrier wave 
that arrives at the antenna. Sometimes the grid speaks 
softly, sometimes loudly; sometimes drawls its com¬ 
mands and sometimes is very peremptory. 

The grid acts as a regulator of the F to P electron 
flow and its action is controlled by the distant signals, 
perhaps 1000 miles away. It regulates the current from 
the B battery, and since this is d. c. the vacuum tube 
acts as a rectifier, changing r. f. a. c. into i. r. f. d. c. 

Precisely as in the explanation of a crystal rectifier, 
the phones repeat to you the sound of the distant signal. 

The Detector. —To call a vacuum tube or a crystal 
a detector is certainly misnaming it. They are not de¬ 
tectives, merely rectifiers or changers, and in the case of 
the vacuum tube, an amplifier. 

An Actual Set. —In Fig. 108 is given the hook-up 
of a receiving set using a vacuum tube. 

The oscillations which are set up in the closed oscil¬ 
lation circuit pass through L, F, G and back to L. 
The direct current interrupted at radio frequency carry¬ 
ing energy changes at audible frequency passes through 
the circuit P, phones F, back to P. 

Should any a. c. leak from the grid to the plate a by¬ 
pass condenser would be needed to shunt this a. c. 
around the phones. The two wires in the telephone 
cord being close together and from 3 to 6 feet long 
form such a condenser. An additional by-pass con¬ 
denser is rarely needed. 

Grid Condenser and Grid Leak. —Many vacuum 
tubes will not operate satisfactorily unless a small con- 


RADIO 


3i3 


denser is placed in the wire to the grid and unless this 
condenser is shunted by a very high resistance called 
a grid leak. 

The grid condenser, by trapping electrons between it 
and the end of the grid, makes the grid very negative, 
when it is negative. This makes the grid shout “Stop.” 
The more completely the grid stops and allows a passage 
to the electrons, the greater the variation in the plate 
circuit current. It is the variations of the d. c. current 
that operate the phones. 



But this condenser will ultimately trap too many 
electrons, making the grid negative all the time. This 
will block the tube so that there is no plate circuit cur¬ 
rent nor could there be any. 

The Grid Leak. —A very high resistance, G L of Fig. 
108, will allow these trapped electrons to leak away at 
a slow rate. 

If the value of grid condenser, about 0.0002 micro¬ 
farads, and the grid leak, about a million ohms, are 
properly balanced, we get the advantages of the grid 
condenser with practically none of its possible bad 
effects. 

The Plate Circuit. —We have talked a lot about 
tuning the open and closed oscillation circuits, but did 












314 THE BOYS’ BOOK OF ELECTRICITY 


not mention the plate circuit. This circuit needs ad¬ 
justing, if we are to get the best results from a receiv¬ 
ing set. 

When the vacuum tube is in operation it acts like a 
generator of interrupted d. c. It is a fact that if a 
generator and a receiver of energy are in a simple series 
circuit, that the greatest possible current will flow if the 
resistances of the generator and receiver are equal. 

For this reason we want phones of high impedance 
to match the high impedance of the tube. It is a queer 
statement but a true one, that phones of high impedance 
are a necessity to force the tube to send a large current 
to the phones. 

Non-Regenerative Receiving.—All the methods 
of reception described so far fall under this heading. 

Regenerative Receiving. —There are two meth¬ 
ods of greatly increasing the strength of the signals as 
heard in the phones. One is by tuned plate circuits and 
the other by a transformer action called a feed back. 

Tuned Plate Circuits. —It will be sufficient now 
to remind you that an interrupted d. c. must build up 
the magnetic fields of its circuit after every interrup¬ 
tion. It therefore acts a little like a. c. 

When a variometer is placed in the plate circuit and 
properly adjusted there is a decided increase in the 
signal strength. 

The Variometer .—A variable inductance is a coil of 
wire so mounted that another coil of wire may revolve 
within it. The coils are connected in series. There is 
capacity between the turns of the coils and between the 
two coils. There is inductance in the coils, which is 
most when they have their axes parallel and least when 
they are at right angles. 

By the rotation of the inner coil the capacity and 
inductance are so altered as to reduce the impedance 
to a. c. to almost zero. 

The Feed Back. —The Tickler .—Another method 


RADIO 


315 


of feed-back or regeneration is by use of a coil in the 
plate circuit arranged so as to be coupled to the closed 
oscillation circuit. Fig. 109 shows how this may be 
done. This is a diagram of what is called incorrectly, 
but yet by almost everyone, a single circuit tuner. 

The coil T in the plate circuit is called a tickler. It 
is pivoted so that it may be rotated, thus increasing or 
decreasing the amount of feed-back. 

The mutual induction between the tickler T and the 
coil L which feeds the electrons to the grid is such that 
when L is sending electrons to the grid, T also pushes 



electrons through L towards the grid, thus resulting in 
a greatly increased charge in the grid. This in turn 
increases the plate current. But this increased current 
passes through the tickler coil T and again acts on the 
coil L. This building up, or feed back or regenerative 
action, goes on until the tube is passing all the filament 
to plate electrons that it possibly can. 

This regenerative action greatly increases the strength 
of the signal as heard through the phones. 

Amplification.—The sets using vacuum tubes 
which have been described might be called a combina¬ 
tion of a tuner, a rectifier and amplifier. But when we 
speak of amplification we usually mean much more 













3i6 THE BOYS’ BOOK OF ELECTRICITY 


amplification than such a combination gives. There are 
two methods. Their names are audio frequency and 
radio frequency amplification. Each amplification ob¬ 
tained by passing the energy through a tube is called a 
step or stage of amplification. 

Audio Amplification. —From any of the sets 
shown in Figs. 108 and 109 remove the phones and put 
a step-up transformer in its place. Connect the sec¬ 
ondary of this transformer to a vacuum tube precisely 
as if the secondary of the transformer were the coil L 



Fig. 110 . Amplification at Audio Frequency. 


of a closed oscillation circuit. You will then have a 
hook-up as in Fig. 110 added to the place where the 
phones were. 

The stream of electrons set in motion by the audio 
frequency transformer A.F.T. of Fig. 110 is a. c. 
The interrupted direct current in the primary of any 
transformer or induction coil causes an alternating cur¬ 
rent in the secondary. 

The oscillations of the electrons from the secondary 
of the audio frequency transformer are impressed on 
the grid and thus control the power from the B battery. 

, The B battery of a detector tube furnishes from 18 to 
• 45 volts, but when used in amplification circuits the B 
battery furnishes from 45 to 90 volts. 














RADIO 


3U 

The grid circuit in such an audio frequency amplifier 
does not need tuning because although but one fre¬ 
quency is imposed upon the currents at a time, in the 
course of one second all the frequencies from 100 to 
3000 are sent into the grid circuit. Tuning would damp 
out some of them. 

No transformer can have the same impedance to all 
frequencies. So some of the audio frequencies are 
weakened, thus distorting the sound which we hear. 

Using an audio frequency transformer suited to the 
vacuum tube used and to the stage of amplification in 
combination with phones of proper impedance we will 
produce the greatest possible signal strength in the 
phones. 

A vacuum tUDe with a very high vacuum is best 
suited for amplifier circuits, for you can use a high 
plate voltage with such tubes. Any ions of gas in the 
tube, as argon, nitrogen or helium, would with high 
B battery voltage conduct electrons from filament to 
grid. This would rob the filament to plate stream of 
electrons, with the result of weakened signal strength 
in the phones. 

Fior the very high amplification to operate a loud 
speaker, the phones in Fig. 110 may be removed and 
another step of audio amplification added. 

Since the distortion of each step is forwarded to the 
next step and amplified, two steps seems to be the prac¬ 
tical limit. 

All the noises of chemical action in the B battery, 
any thermal electrical effects from unequal heating of 
the joints and connections in the set make noises, and 
these are amplified. This also makes more than two 
steps unwise. 

C Battery .—We do not use a grid condenser and a 
grid leak in amplification circuits. A leak that would 
operate properly for a frequency of 1000 would leak 


3 i8 THE BOYS’ BOOK OF ELECTRICITY 


too fast for 200 cycles a second and not fast enough 
for 2000 cycles a second. 

Since in a audio amplification grid circuit we are 
handling frequencies from 100 to 3000 the grid con¬ 
denser and grid leak will not do. 

A result similar to the grid condenser is performed 
by a voltage of 3 volts applied in the grid circuit. This 
is called the C battery and is said to give “the proper 
negative potential to the grid.” 

Amplifiers that you purchase do not use a cell or 



Fig. 111. Amplification at Radio Frequency. 


cells to furnish the C battery voltage. In them the 
principle shown in the reducer in Fig. 6 is used. 

A small portion of the drop through the filament 
rheostat is used instead of a cell. Whenever a differ¬ 
ence of pressure exists, that drop, as we call it, will 
act as a cell and furnish voltage. 

Radio Frequency Amplification. —This means 
amplification of the incoming energy at radio frequency. 
There are many carrier waves in the ether, and we wish 
to keep out all but the desired one. For this reason 
the absorbing circuit and the one to which the energy 
is transferred should be tuned. 

The incoming signals affect the grid of a vacuum 
tube and it operates in the same manner as an audio 















RADIO 


3 X 9 

frequency amplifier except that the energy handled is 
at radio frequency. The B battery should furnish from 
90 to 110 volts to a hard vacuum tube. 

Less energy will be used up if the impedance of the 
plate circuit is made almost zero by proper tuning. 



The output of a radio frequency amplifying set may 
be transferred in two ways, to a detector tube circuit 
where it is changed to d. c. at audio frequency. An 
oscillation transformer with no step-up in voltage may 
be used or one with a step-up in the voltage. 

Transformers for audio frequency work are not suit¬ 
able for the high frequencies of the carrier waves. For 











320 THE BOYS’ BOOK OF ELECTRICITY 


radio frequency amplification only those transformers 
designed for this special purpose and for a particular 
range of wave lengths should be used. See Fig. 111. 

Variable Condensers. —The small fixed capacity 
condensers may be made of tinfoil or copper foil with 
mica as the dielectric. The condensers of variable 
capacity used for tuning are constructed with aluminum 
plates and use air as the dielectric. 

Rotation of the movable plates in between the sta¬ 
tionary plates increases the capacity and tunes the cir¬ 
cuit, of which the condenser is a part, to longer wave 
lengths. Fig. 112 shows such a variable condenser. 

Building Receiving Sets. —Start with a crystal 
set. Send ten cents in silver to the Commissioner of 
Public Documents, Washington, D. C., asking for a 
copy of the Bulletin No. 120 of the Bureau of 
Standards. 

When you want a receiver that will respond to weaker 
signals, build a vacuum tube set. Go to a reputable 
dealer and talk to him; let him see that you know what 
you have read in this book. He will then know that he 
can talk radio to you, rather than about knobs and 
mahogany boxes. 

Buy the materials to build the set the hook-up of 
which is shown in Fig. 109. He will probably wish 
to sell you the coils L and T in one unit, which is the 
best plan. 

Until you are experienced beware of circuits named 
after some man. Beware of supers, reflexes, variable 
grid leaks. Some day you will handle them with ease, 
but at the beginning of your experiments they will 
make your set very complicated and perhaps you will 
be unable to make it work. 

Reading Radio Hook-ups.—The wiring diagrams 
use symbols which must be translated into English be¬ 
fore you know what to buy and how to wire them. 
Fig. 113 will enable you to translate diagrams. 


RADIO 


321 


ANTENNA 
BATTERY -f 
CONDENSER : 


r 


OR OR 

1 - 

VAR/ABLE CONDENSER 


JL 


" 7 * 


CONNECTING WIRES 


NO CONNECTION 


COUPLED COILS a 
CRYSTAL DETECTOR 


VARIABLY COUPLED OR 
VARIOCOUPLER 


- 03 - 


GRlD LEAK AND GRID CONDENSER 




INDUCTANCE TWSVST VARIABLE INDUCTANCE TfWf 
LOUD SPEAKER □<d) 

TELEPHONE RECEIVERS, ’PHONES OR HEAD SET 6 b 

TELEPHONE TRANSMITTER 

AUDIO FREQUENCY TRANSFORMER ||jjj| 

RADIO FREQUENCY TRANSFORMER § S§ 



OR 


VACUUM TUBE 
VARIOMETER 

Fig. 113. Standard Symbols Used in Radio Wiring Diagrams. 























322 THE BOYS’ BOOK OE ELECTRICITY 


SIGNING OFF 


This is station S. A. S. International Writo-phone 
Station of E. P. Dutton & Company, at New York , 
N. YU. S. A. 

The hook you have just read was broadcast from our 
author's laboratory by the publishing establishment erf 
E. P. Dutton & Company. 

Please stand by until our next book. 


GOOD NIGHT, 



GLOSSARY 


A Battery.—A battery furnishing current for the filament of a 
vacuum tube. 

a. c.—An abbreviation for alternating current. 

Alpha particles.—When two electrons and four protons are 
thrown out, in a compact group, from a nucleus, we call the 
group an alpha particle. 

Amalgam.—An alloy or mixture of metals, one of which is 
mercury. Iron does not form an amalgam. 

Ampere-hour.—One ampere for one hour. Two amperes for 
half an hour, or any such combination. The unit of work 
that a storage battery will do. 

Analogy.—A resemblance between things otherwise quite 
different. Like the flow of water and electric current. 

Antenna.—A long straight wire or wires collecting or radiat¬ 
ing electrical energy. 

Atom.—A nucleus surrounded by half as many electrons as 
there are protons in the nucleus. There being an equal 
number of electrons and protons in the atom it is neutral, 
that is, electrically unchanged. 

Armature.—A core of iron surrounded by coils of insulated 
wire, revolving near the poles of a magnet, in a dynamo. 
Also a movable piece of soft iron placed in front of a pole 
piece of a magnet, so that it can be attracted by the magnet. 

Battery.—A group of cells considered as a unit. Usually 
only two wires lead from a battery to the work. 

B Battery.—A battery, usually of dry cells, furnishing from 
16^4 up to 11 2 x / 2 volts for the plate circuit of a vacuum tube. 

B. C. L.—A broadcast listener who is not interested in in¬ 
tercommunication by code. B. C. L. frequently know noth¬ 
ing about radio nor care about it, being merely knob 
turners. 

Beta particles.—The electrons which are shot out one by one 
from the nucleus of some atoms. Electrons given up or 
taken from the outer swarm of electrons of an atom are 
not called beta particles. 

Blow.—Slang word used for melt. We say that a fuse blows. 

Bore.—The bore of a tube is the hole inside of it. 

Brass Pounder.—A telegrapher. 

323 


324 THE BOYS’ BOOK OF ELECTRICITY 

B. T. U. —British Thermal Unit. The amount of energy in 
the form of heat that will raise 1 pound of water 1 degree 
Fahrenheit. 

B. X. —Two wires of size No. 14 or larger, insulated with rub¬ 
ber and cotton, then enclosed in a flexible metal armor. 

Calorie. —The amount of energy in the form of heat that will 
raise 1 gram of water 1 degree Centigrade. 

Carrier wave. —A continuous wave sent out as long as the 
station is transmitting. This wave of very high frequency 
cannot cause voice or music at the receiving station, but 
acts as if it carried certain modulations. These are the 
cause of the voice or music. 

Cell. —A single unit of a battery. 

Condenser. —A device for accumulating electrons by their 
mutual actions from one conducting plate to another, 
through an insulator called a dielectric. Condensers ob¬ 
struct d. c. but allow a. c. to pass. 

Constant. —Steady. Not changing. A special number. We 
speak of the constants of a circuit. We say that 746 watts 
are equivalent to a horsepower. 746 is a constant. 

Combined resistance.—The effective resistance of any combi¬ 
nation of resistances. Usually refers to the effective resist¬ 
ance of several resistances in parallel. 

Cord. —When used in the phrase “lamp cord” means a pair of 
flexible copper wires properly insulated and bound into one 
cord by cotton or silk threads. 

Current.—A flow of electrons through a definite path. The 
direction of the current is, by agreement of scientists, said 
to be in the opposite direction to that in which the electrons 
are moving. We say the current flows from the + to the —, 
while we know that the electrons flow from the — to the 
+. See Fig. 41. 

Cycles.—Repetitions of anything in exactly the same way. 
One cycle is one round trip back to the start and all ready 
to do it again. 

Damped.—Means diminished. 

d. c.—An abbreviation for direct current. 

Deflection.—When the pointer of a galvanometer or other 
meter moves over to a reading and stays there, we call this 
action “a deflection.” 

Dielectric.—An insulator specially adapted to be used as the 
insulator between the plates of a condenser, for it opposes 
the passage of electrons yet allows the force caused by 
electrons to pass through it. 


GLOSSARY 


325 

Dowel rod.—A cylindrical rod of hard wood. May be ob¬ 
tained in many sizes of diameters. 

Electrode. —That part of a solid conductor thrust into a liquid, 
a gas or a vacuum is called an electrode. The electrode is 
usually a plate or rod of some different material connected 
to the copper conductors. 

Electrolyte. —A liquid conductor whose atoms have sepa¬ 
rated into groups carrying electrical charges. These 
groups are called ions. 

Electromotive force.—The pressure developed to push elec¬ 
trons. An electron motive force. 

Electron. —A tiny speck of negative electricity. Electrons, 
protons and energy make up the materials of our world. 

Emanation. —When alpha particles are shot out of radium, 
a product is formed by these alpha particles called radium 
emanation. 

Energy. —The motive power that makes things move and 
keeps them moving. Energy added to electricity makes the 
substances of our world. 

Erg. —About one thousandth part of the work needed to lift 
one gram up from the earth, vertically, for one centimeter. 
Two grams moving at a speed of one centimeter a second 
can do one erg of work. 

Ether.—An imaginary substance which, if it does exist, fills 
all the spaces where there is no material. 

Fan. —A B. C. L. who follows radio closely. 

F. b. o. m. —Fine business old man. The radio amateur’s way 
of expressing approval. 

Feeder. —A conductor carrying current to and from the sub¬ 
sidiary or branch circuits. Apparatus is not connected to 
feeders. 

Filament.— (Of a lamp.) A thin wire. 

Flux.—1. A material which cleans metal, so that solder may 
adhere. 2. The flux or flow of magnetism through a mag¬ 
netized space. 

Frequency. —The number of vibrations or oscillations in one 
second. Divide the speed by the wave length to obtain the 
frequency. 

Fuse.—A wire, bar or strip of lead or some readily melting 
alloy which melts (blows) when a current passes through it 
stronger than that for which it was designed to carry. 

Ground. —1. A term applied to the earth as a conductor. 2. 
An accidental or undesired connection between a circuit, 
line or apparatus and the earth. 


326 THE BOYS’ BOOK OF ELECTRICITY 


Ham.—Originally meant a “brass pounder” with a fist like a 
ham. Now applied to persons regularly engaged in wire¬ 
less telegraphy for the love of the work. The “hams” sent 
and received 160,000 messages in March, 1923. 

Hook-up. —A wiring diagram showing the electrical connec¬ 
tions and relative positions of apparatus. 

Hydrometer.—An instrument for determining the specific 
gravity (density) of liquids. The lighter the liquid the 
deeper the hydrometer sinks. 

Insulators.—Substances which conduct so poorly that we use 
them to confine electricity along certain paths or in certain 
places. At high pressures insulators conduct slightly. 

i. r. f. d. c.—See after r. f. a. c. 

Ion. —An atom, molecule or radical which, having gained or 
lost electrons, has become electrically charged. 

Isotope. —A substance which to a chemist is the same as one 
or more other substances, but to an electrical investigator 
is different from them. Isotopes differ only in their nuclei. 

Jack. —A device consisting of one or more strips of metal 
held in insulation. It may close or open circuits or do both 
when the plug is inserted. 

Joint resistance. —The same as combined resistance. 

Juice.—A slang word for current or flow of electrons. 

Kick. —(Of a galvanometer.) When the pointer moves over 
to a reading and immediately falls back to zero, we call it 
a kick. The number to which it “kicks” we call the reading. 

Kinetic energy. —The work that electricity can do because it 
is in motion. 

Kink.—(In a wire.) See Fig. 7. 

Laminated.—Consisting of thin layers. 

Lay-out.—A paper pattern on which all the apparatus is ar¬ 
ranged in full size and actual shapes. It shows the wiring 
according to the hook-up and the holes to be drilled to 
mount the apparatus. 

Lead-in.—A wire or wires from the antenna to the receiving 
set. 

Loud speaker.—A specially designed telephone receiver com¬ 
bined with a horn. 

Lug.—A piece of metal to be soldered to a wire and its other 
end clamped under a binding post or switch terminal. Used 
to make a strong mechanical and good electrical connection. 

Mass. —Electricity has, besides its electrical qualities, an¬ 
other separate and distinctly different property called 
mass. Mass is that which makes bodies hard to start and 
hard to stop. 


GLOSSARY 


327 


Modulations.—Changes in the amount of energy in a carrier 
wave. 

Molecule. —A group of atoms joined by electrical forces. In 
it are an equal number of protons and electrons, hence 
electrically it is neutral or uncharged. 

Multiple.—Older name for “parallel.” 

Nucleus.—Some protons and half as many electrons in a 
compact body at the center of an atom. 

On.—A slang term for “connected to” or “in the circuit with.” 

Open circuit.—A break or very high resistance in a circuit, 
making it useless for the work required of it. 

Orbit.—The path along which a body moves in getting back 
to the place from which it started. 

Oscillate.—Means vibrate. 

Parallel.—Indicates that the current splits and a different part 
of it passes through all the parts of the circuit that are in 
parallel. 

Permeability.—The relative ease with which magnetism 
passes through a material. 

Plug.—A device to push against the strips of a jack and thus 
move them. This causes them to make the proper contacts. 

Permanent magnet. —A magnetized piece of hard steel which, 
due to its retentivity, will continue to be a magnet for a long 
time. 

Phenomenon. —(Plural phenomena.) Some action that you 
can see, feel, hear or observe in some way. Not used in 
science with the meaning of unusual or extraordinary. 

Power-house. —A name given to a place where electrical 
power is generated. 

Primary cell.—A cell which, like a tobacco pipe, must be re¬ 
filled with the same chemicals that were originally in it 

Proton.—The tiny speck of positive electricity. 

Quantum.—(Plural quanta.) The tiny amount of energy 
radiated at one time. Energy is not radiated continuously 
but in quanta. The size of a quantum changes with the 
frequency of the oscillations of the electrons radiating the 
energy. 

Radiation.—Energy travelling through space by itself. 
Energy often travels on substances. It is also radiated 
from substances and is then called radiation. 

Radical.—A group of atoms which in ordinary chemical ac¬ 
tions does not separate. Neutral or unchanged radicals can 
only exist when combined with something. Radicals not 
in combination are charged and are called ions. 


328 THE BOYS’ BOOK OF ELECTRICITY 

Radioactive.—The nuclei of some substances explode, throw¬ 
ing off protons and electrons. In this way radioactive sub¬ 
stances change to new substances. 

Reads.—Slang for “indicates.” 

Rectifies.—Chances a. c. to d. c. 

Resistance coil.—A long wire coiled up to occupy less space, 
which resists the passage of electrons. 

Resin.—The sticky part of the sap, or made by the sap of 
trees, which hardens on exposure to air. Rosin is resin 
from the long leaf pine tree. 

Resonance.—See Tuned circuits. 

Retentivity.—When a material keeps some magnetism after 
the magnetizing force is removed. 

r. f. a. c.—An alternating current, the number of cycles per 
second of its electrons being very high. 

i. r. f. d. c.—A direct current interrupted at radio (high) fre¬ 
quency. 

Rheostat.—A variable resistance. 

Rosin.—See Resin. Used as a flux in soldering. Also to 
make sealing wax. 

Series.—Indicates that the same current passes through all 
the parts of the circuit that are in series. 

Set-up.—The actual apparatus arranged and electrically con- 

< nected according to the hook-up. 

Shellac.—Made by insects. Looks like a resin. Dissolved in 
alcohol it makes a quick drying, insulating varnish. 

Shunt.—A shunt on an electrical circuit is like a side track on 
a railway. It carries the electrons around a certain place 
in the main line. 

Solenoid.—A coil of wire carrying current. An air core elec¬ 
tromagnet. 

Static.—1. An electrical charge which stays where it was 
formed. A few electrons at very high pressure. 2. Atmos¬ 
pheric or ground charges which affect a radio receiving set. 

Storage cell.—A cell in which the original chemical may be 
restored by passing a current of electricity through it. 

Specific.—Means special. 

Takes a current.—Slang for “permits a current to pass.” 

Temporary magnet.—A magnetized piece of soft iron which, 
due to its low retentivity, will become demagnetized as 
soon as it is removed from the magnetic field. 

Tension.—Used in phrases “high tension,” “low tension,” it 
means voltage. 

Time constant.—The fraction of a second which an electron 
needs to make one oscillation in a particular circuit is called 
the time constant of that circuit. 


GLOSSARY 


329 , 


Transformer.—A device operated by magnetism which, with¬ 
out any electrical connection between the two circuits, 
transfers alternating current power from one to the other. 
It usually changes the voltage. 

Tuned circuits. —When the combination of inductance and 
capacity in a circuit is adjusted to offer the least possible 
resistance to a certain frequency, we say the circuit is 
tuned. When two circuits are tuned to the same frequency 
we call them tuned circuits. They are also in resonance. 

Turbine. —A modern and efficient form of water wheel. Also 
a similar device using steam at the motive power. 

Vacuum. —A space from which all the known materials have 
been removed. As far as we can determine by all sorts of 
tests, a vacuum is empty. 

Voltage. —The pressure exerted by a cell, dynamo, etc., on a. 
stream of electrons. 









INDEX 


A 

A battery, 310 
Agonic lines, 208 
Alternating current, 49 
Alternator, 218 
Amalgamation, 112 
Ampere, 130 
Ampere-hour, 126 
Ampere-turns, 199 
Amplification, 315 

Audio, 316 
“ Radio, 318 
Amplitude, 284 
Antenna, 295 
Armature, 222 
Atmospheric electricity, 63 
Atoms, 41, 44 
Audio frequency, 50 

B 

Back E. M. F., 256 
B battery, 310 
Batteries, 118 
Bell, 243 
“ troubles, 245 
“ control, 246 
Bichromate cell, 114 
Boosters, 231 
Bound charge, 87 
Buzzer, 248 

“ telegraph, 248 

c 

Capacity, 86, 90 
Carrier wave, 304 


C battery, 317 
Cells, 102, 118 
Charges, 46 
Circuits, 135, 146, 151 
Combined resistance, 153 
Commutating switch, 239 
Commutator, 221 
Compass, 208 
Condensers, 82 

“ Variable, 320 
Conductors, 173 
Consequent poles, 196 
Control panel, 165 
Cores, 197, 222 
Coulomb, 129 
Critical, 300 
Crow-foot cell, 115 
Crystal, 305 
Cycles, 50 

D 

Declination, 208 
Detector, 312 
Dielectric, 90 
Dip, 209 

Direct current, 49 
Divided circuits, 151 
Drop, 159 
Dry cell, 119 
Dynamo, 220 
Dynamotor, 232 

E 

Edison cell, 125 
Electromagnetic waves, 285 
Electromotive force, 117 


332 


INDEX 


Electrons, 40, 46 
Electrophorus, 75 
Electroscope, 72 
Energy, 56 
Ether, 294 

F 

Fan, Electric, 256 
Farad, 88, 133 
Feed back, 314 
Field, Dynamo, 223 
“ Magnetic, 203 
Filament, 308 
Flux, 200 
Franklin, 63 
Free charge, 87 
Frequency, 50 

G 

galvanometer, 211 
Galvanoscope, 21 
Generator, 220 
Grier, 311 

“ condenser, 313 
“ leak, 313 
Gravity cell, 115 
Ground, 136 

H 

Henry, 133 
Hook-ups, 16 

I 

Ignition, 270 
Impedance, 291 
Incandescent lamps, 291 
Inclination, see Dip 
Induced currents, 216 
Induction coil, 268 
Induction, Electromagnetic,215 
Interference, 300 


Ir, 159 

Iron, Electric, 254 
Isotopes, 60 
I square R, 157, 184 

J 

Joule’s Law, 156 
Juice, 48 

K 

Kilowatt, 134 
Kilowatt-hour, 134 
Kinetic energy, 56 

L 

Leyden jar, 77 
Lightning, 65 

“ rods, 66 
Lines of force, 200 
Local action, 112 
Lodestone, 191 
Loud speaker, 299 

M 

Magnets, 191 
Magnetic substances, 197 
Measuring pressure, 30 
quantity, 33 
resistance, 177 
Microfarad, 88 
Microhenry, 133 
Modulation, 304 
Motors, 225 
“ A. C„ 230 
“ dynamo, 232 
Induction, 238 
“ Series, 230 

“ Shunt, 229 

“ Reversal of a, 231 
Universal, 231 


INDEX 


333 


N 

Nitrogen lamp, 252 

0 

Ohm’s Law, 149 
P 

Parallel, 33, 138 
Permeability, 198 
Plate, 311 

Polarity Indicator, 168 
Polarity, Rules for, 195 
Polarization, 114 
Poles, 193 
Pole changer, 238 
Polyphase A. C., 238 
Potential energy, 56 
Primary cells, 120 
Protons, 46 

Q 

Quanta, 57 

R 


Selectivity, 302 
Series, 10, 136 
“ parallel, 138 
Sharp, 300 
Short Circuit, 137 
Shunts, 137 
Shunt dynamo, 224 
Smashing point, 252 
Soldering, 9 
Solenoid, 193 
Speed regulation, 256 
Staircase lamps, 252 
Starting box, 257 
Static, 48, 60, 69 
Storage cells, 121 

T 

Telegraph, 261 
Telephone, 262 
Three wire circuit, 162 
Thunder Storms, 65 
Tickler, 314 
Tools, 3 

Transformer, 234 
Tuning 302 
Tuners, 300 
Two wire circuit, 160 


Radio frequency, 50 
Radio frequency amplification, 
318 

Radio waves, 285 
Reactance, 288 
Reducer, 15 
Regeneration, 314 
Resistance, 179, 183 

“ Laws of, 185 
Retentivity, 199 
Rotary converter, 232 

S 

Safety device, 11 
Saturation, 200 
Self induction, 288 


U 

Underwriters, 175, 183 
V 

Vacuum tube, 308 
Variometer, 314 
Volt, 133 
Voltage, 117 


W 

Watt, 133 

“ meter, 248 
Waves, 280 

“ length, 283 
Wires, 174 

“ tables, 181 


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